pre test examinationpre test examination · 2020-04-27 · baud rate: in case of data communication...

Pre Test ExaminationPre Test ExaminationPre Test ExaminationPre Test Examination

SyllabusSyllabusSyllabusSyllabus

Subject Computer ScienceSubject Computer ScienceSubject Computer ScienceSubject Computer Science

Class XIIClass XIIClass XIIClass XII

1 Sequential Logic Circuits

2 Computer Networking

3 Database Management System

A G Sir

Computer Networks

What is a computer Network

A network is any collection of independent computers that communicate with one another over a shared network medium A computer network is a collection of two or more connected computers When these computers are joined in a network people can share files and peripherals such as modems printers tape backup drives or CD-ROM drives When networks at multiple locations are connected using services available from phone companies people can send e-mail share links to the global Internet or conduct video conferences in real time with other remote users When a network becomes open sourced it can be managed properly with online collaboration software As companies rely on applications like electronic mail and database management for core business operations computer networking becomes increasingly more important Every network includes

bull At least two computers Server or Client workstation bull Networking Interface Cards (NIC) bull A connection medium usually a wire or cable although wireless communication

between networked computers and peripherals is also possible bull Network Operating system software such as Microsoft Windows NT or 2000 Novell

NetWare Unix and Linux

Importance of networking 1gt Resource sharing Without depending on where the computers are data can be shared

between the users

2gt High Reliability Data are stored in more than one machines because if one source is

crashed then the data can be accessed from another source So there is high

reliability

3gt Saving Money Using main frame computer system very much costly That is why network

system is used commonly

4gt Security In network system there is enough security No one can erase data easily

Some topics related to network i) Terminal Any input-output device used to send and receive data in a network

system is known as terminal Example Computers telephone Fax machine Sound box

etc

ii) Telecommunication Processors These are devices which support data transmission

and reception between terminals and computers Example Modem Multiplexers Front-

end Processor etc

iii) Telecommunication Channel and Media The media over which data are transmitted

and received are called Telecommunication Channel Example Optical Fiber Cable

Radio wave etc

iv) Computer Besides the micro computers used by the end user the computers are

used to send or processing information Various types of computers are used in

network

v) Telecommunication Software Telecommunication software consists of programs

These reside in host computer systems communication control computers and end user

computers

Data Signal Data are sent in the form of electrical signals in computer network Electrical signal means change of voltage with change of time When voltage is zero and

then the voltage gradually increases and reaches the maximum point then there is a

change in voltage After that it goes down with the decrease of voltage

Bandwidth Bandwidth is the difference between highest and lowest frequency in a

transmission medium It is the measure of how much data can be transmitted per second in

a particular transmission medium The unit of bandwidth for analog data is Kilohertz

(KHz) and for digital data are Kbps Mbps Gbps etc

Baud Rate In case of data communication Baud rate is the measure of number of times the

signal changes its value (voltage) Therefore baud rate is the measure of signaling

speed

Communication Media It is a physical channel between transmitter and receiver in a data transmission system It

interconnects source with destination Transmission media is divided in two classes

1gt Bounded media (Guided Media)

2gt Unbounded Media (Unguided Media)

Bounded Media In bounded media the waves are guided along a solid medium like copper wire Bounded media use electrical cables or optical cables

Coaxial Cable

A coaxial cable consists of many small cables in a protective cover The cover shields the

cable from physical dangers as well as from electromagnetic interference Within the cover

the various cables are shielded from interference with one another Coaxial cables are used

in communication networks that require many simultaneous communication links Each coaxial

cable can provide more than 5000 links

Coaxial cable is a two-conductor cable in which one conductor forms an electromagnetic

shield around the other The two conductors are separated by insulation It is a constant

impedance transmission cable This media is used in base band and broadband transmission

Coaxial cables do not produce external electric and magnetic fields and are not affected by

them This makes them ideally suited although more expensive for transmitting signals

There are two types of coaxial cables baseband and broadband A baseband coaxial cable

transmits a single signal at a time at very high speed A broadband coaxial cable can

transmit many simultaneous signals using different frequencies A baseband cable is mainly

used for LANs A broadband coaxial cable can carry only an analog signal So it must be

used with a modem

Baseband coaxial cables are 50 ohm cables used for digital transmission For 1Km cables

the bandwidth is 1-2 Gbps Longer cables can be used with low data rates or periodic

amplifiers Broadband coaxial cables are 75 ohm cables used for analog transmission They

use standard cable television technology To transmit digital signals on an analog network

each interface must have converters ie analog to digital for outgoing bit stream n vice

versa another difference bw baseband and broadband is that broadband systems have

developed dual cables Since broadband is used for large area it requires amplifiers which

are unidirectional In dual band systems two identical cables run together one used for

outgoing data one for incoming data Different bandwidths are given for inbound and

outbound cables Eg for 300MHz 5-30MHz for inbound and 40-300MHz for outbound

Features

bull It provides better immunity than twisted pair

bull This cable is able to transmit data at higher rates

Limitations

bull High installation cost

bull High maintenance cost

b) Twisted-Pair cable

Twisted-pair cable is made up of pairs of copper wires twisted together in precisely

calculated fashions The wires carry more information when twisted Two varieties of

twisted-pair cable are

bull shielded twisted-pair cable

bull Unshielded twisted-pair cable

1)Shielded twisted-pair cable

Shielded twisted-pair cabling is more

thoroughly insulated or shielded This cabling

is more reliable and expensive It is easy to

install The twisted pair varies in quality and

capacity Quality and capacity depend upon the

number of twists per inch and how much

insulation it has By twisting the wires around

one another electromagnetic interference from

external sources is reduced By adding

shielding twisted pair is capable of

transmitting data at higher rates

2)Unshielded twisted pair cable

In unshielded twisted pair cabling the twisted pair cable is not shielded Some

organizations use existing telephone wiring for their LANs This telephone wiring is

usually unshielded twisted pair cable

The main disadvantage associated with this is low noise immunity During a telephone

conversation noise and interference from other electronic equipment takes the form of

static and is rarely loud enough to disrupt the call

But that same line can scramble a data transmission and require the sending device to

retransmit An excessive number of such retransmissions will reduce network efficiency

Features of twisted-pair cables

bull Inexpensive

bull Easy to install

bull Easy to tap

bull Can accommodate up to 1000 devices

Limitations

The network coverage area is between 300 feet and 1000 feet only

c) Fiber- optic cable

A fiber-optic cable consists of strands of glass-like thread Through the use of a

laser data are transmitted from one end of a cable to the other Fiber optic cables will

increase the capacity of like-sized coaxial cables by at least a factor of 10 This makes

them valuable for use in a variety of applications mainly in communication network

Features

bull Huge bandwidth

bull Optical fiber systems are not affected by external noise

bull The error rate for the data transmitted across fiber optic cable is very low

Limitations

bull Cost is high

bull Fibers fragility makes it more difficult to handle

Unbounded MediaWireless communication

1gt Radio Communication Radio frequency transmission deals with frequency in order of

30 MHz Below 30 MHz frequency reflected towards the earth due to ionospheric

characteristics whereas above 30 MHz propagation of signal is on the line of sight

path To increase the distance antennas are placed in between line of sight paths

In radio communication data transfer rate is about 100 ndash 400 Mbps

2gt Microwave Communication Microwave systems transmit high speed microwave signal in

a line of sight path between relay station space The waves can not bend with the

curvature of the earth So microwave links would in variable use line of transmission

along ground route by repeater station placed 100 ndash 200 Km apart The repeater copies

or repeats the signal and amplifies all the signals before retransmission Microwave

signals are relayed by antennas usually placed on the top of the buildings towers

hills and mountain peaks The data transfer rate through microwave link is about 1000

Mbps

3gt Communication Satellites Communication Satellites in space orbiting 22000 miles

above the earth are also used as microwave relay stations These rotate at precise

point and spread above the equator so that these appear stationary to microwave

transmitters on the ground An artificial satellite which appears stationary to an

observer on the earth is called geostationary satellite When such a satellite is

used for communication purpose is called communication on satellite The

communication satellite usually acts as a reflector It accepts the signals from one

point of the earth and returns the same signal to some other points on the earth

Data Transmission Modes

There are three transmission modes

1gt Simplex Transmission In this mode data is transferred in one direction only

and never in opposite direction It is suitable for receive only printers

These devices do not transmit information Example Communication between

keyboard and computer

2gt Half-duplex Transmission In this mode data is transferred in both direction

but not simultaneously Example Communication between Computer and disk

3gt Full-duplex Transmission In this mode data can be transferred in both

directions simultaneously Example Telephone

Several Ways of Transmitting Signal

Parallel Transmission Digital computer only understands binary digits (bit) ie lsquo0rsquo and lsquo1rsquo So in computer network data are sent in the form of bit stream (combination of lsquo0rsquos

Data Transmission

Parallel Serial

Asynchronous Synchronous

and lsquo1rsquos) When n numbers of bit of a n bit data are sent simultaneously then the transmission is called Parallel Transmission Advantage All the bits are sent at a time So the speed of transmission is very high Disadvantage For n bit data there is n number of communication channels are needed Serial Transmission In case of serial transmission only one communication channel is used and all the bits are sent through that channel one after another Advantage i) Only one channel is required ii) Not costly iii) Very useful for long distance Disadvantages i) Speed of transmission is much slower than Parallel Transmission ii) Data have to wait long time in data-queue iii) Time consuming 1gt Asynchronous Transmission According to Serial transmission in case of Asynchronous

transmission bits are sent one after another In this case characters (Generally of 8 bits ) are send on at a time Every character starts with a Start bit which is denoted by lsquo0rsquo After the start bit the 8 bits of character are sent After that a parity bit is sent for error detection if any Then stop bit is sent which is denoted by lsquo1rsquo After that the start bit of another character is sent When no character is sent then the communication channel is in idle situation which is in binary lsquo1rsquo situation (presence of negative voltage in line) In case of Asynchronous transmission timing problem can be avoided

2gt Synchronous Transmission Synchronous transmission is one type of Serial Transmission In this case a block of bits is transmitted without start and stop bit in the form of long frame There is no space between two frames

Difference between Asynchronous and Synchronous Transmission

Asynchronous Transmission Synchronous Transmission

i) Every character is sent separately ii) At the beginning and end of every character there is start bit and stop bit

iii) Constant bit rate iv) No limit of block length v) Low speed communication vi) Synchronisation errors results in loss of only one characters

i) Characters are sent like in the form of block

ii) There is no start bit or stop bit

iii) Constant bit rate over a block iv) Block length is fixed v) High speed communication vii) Synchronisation errors results in loss of complete block

Switching According to demand switch is needed to construct connection between two points in a network The construction of the said connection is called Switching There are three types of Switching

i) Circuit Switching It analogous to a simple telephone call When telephone call is made then the switching instruments of the telephone system search for physical link between sender and receiver telephone This technology is circuit switching technology The line is available for the duration of the call At the end of the

call circuit is broken and another location can be dialed and new circuit is established

ii) Message Switching In this type of switching technology no physical link between sender and receiver is needed Instead of that at first the data of the sender are stored in router in the form of block Then the blocks are sent by the router one after another Every block is received by router router examines for error and resends In case of message switching there is no fixed length for blocks Disk is needed to store long block in router and the blocks may wait for long times in router

iii) Packet Switching The problems in message switching can be overcome by Packet switching In this case there is maximum size for the blocks and they are called packets So there is no need for disk because it can be stored into the main memory of the router The advantages of packet switching over message switching are

1 The first packet of message containing many packets will be sent to receiver without depending on the second packet`s situation Therefore receiving and sending message can be done simultaneously by the router

2 It can avoid network congestion

Types of Networks Computer Networks fall into three classes regarding the size distance and the structure

namely LAN (Local Area Network) MAN (Metropolitan Area Network) WAN (Wide Area Network)

A LAN links a small group of functionally similar workstations within a local geographic

area such as a series of adjacent cubicles or offices on the same floor Once the Computer

network expands to include other floors or divers office within a metropolitan area it

becomes a MAN Finally a WAN is simply a LAN of LANs WANs expand the boundaries of

computer networking to a global or even galactic scale

LAN (Local Area Network)

A Local Area Network is a computer network covering a small Networks geographical

area like a home office or groups of buildings eg a school Network For example a

library will have a wired or wireless LAN Network for users to interconnect local

networking devices eg printers and servers to connect to the internet The defining

characteristics of LANs Network in contrast to Wide Area Networks (WANs) includes their

much higher data-transfer rates smaller geographic range and lack of need for leased

telecommunication lines Smaller Networks generally consist of a one or more switches

linked to each other - often with one connected to a router cable modem or DSL modem for

Internet access LANs Network may have connections with other LANs Network via leased

lines leased services

MAN (Metropolitan Area Network)

MAN stands for Metropolitan Area Networks is one of a number of types of networks A MAN (

Metropolitan Area Networks ) is a relatively new class of network MAN is larger than a

local area network (LAN) and as its name implies covers the area of a single city MANs (

Metropolitan Area Networks ) rarely extend beyond 100 KM and frequently comprise a

combination of different hardware and transmission media

The two most important components of MANs ( Metropolitan Area Networks ) are security and

standardization Security is important because information is being shared between

dissimilar systems Standardization is necessary to ensure reliable data communication

A MAN ( Metropolitan Area Networks ) usually interconnects a number of local area networks

(LANs) using a high-capacity backbone technology such as fiber-optical links and provides

up-link services to wide area networks (or WAN) and the Internet

MAN ( Metropolitan Area Network ) adopted technologies from both LAN (local area network)

and WAN (Wide Area Network) to serve its purpose Some legacy technologies used for MAN

( Metropolitan Area Network ) are ATM FDDI DQDB and SMDS These older technologies are in

the process of being displaced by Gigabit Ethernet and 10 Gigabit Ethernet At the physical

level MAN links between LANs (local area networks) have been built on fiber optical cables

or using wireless technologies such as microwave or radio

The Metropolitan Area Networks (MAN) protocols are mostly at the data link level (layer 2

in the OSI model ) which are defined by IEEE ITU-T etc

WAN (Wide Area Networks)

A wide area network (WAN) is a telecommunication network A wide area network is simply a

LAN of LANs or Network Of Networks WANs connect LANs (Local Area Networks) that may be on

opposite sides of a building across the country or around the world WANs (wide area

networks) are characterized by the slowest data communication rates and the largest

distances WANs (wide area networks) can be of two types an enterprise WAN (wide area

networks) and Global WAN (wide area networks)

Computers connected to a Wide Area Networks are often connected through public networks

such as the telephone system They can also be connected through leased lines or

satellites The largest WAN (wide area networks) in existence is the Internet Some

segments of the Internet like VPN (Virtual Private Networks) based extranets are also

WANs (wide area networks) in themselves Finally many WANs (wide area networks) are

corporate or research networks that utilize leased lines

Numerous WANs have been constructed including public packet networks large corporate

networks military networks banking networks stock brokerage networks and airline

reservation networks

Campus Area Network (CAN)

A campus area networks (CANs) is a computer network interconnecting a few local area

networks (LANs) within a university campus or corporate campus Network Campus area network

may link a variety of campus buildings A campus area network is larger than a local area

network but smaller than a metropolitan area network (MAN) or wide area network (WAN)CAN

can also stand for corporate area network

Topology

The term Computer Network topology defines the geographic arrangement of computer

networking devices It describes the actual layout of the computer network hardware Given

the location of workstations and peripherals the goal of topology is to find the most

economical and efficient way to connect all the users to the computer network resources

while providing adequate capacity to handle user demands maintain system reliability and

minimize delay Basic Types of Topology

There are six basic types of network topologies in the study of network topology bus

topology ring topology star topology hybrid topology mesh topology and tree topology

The interconnections between computers whether logical or physical are the foundation of

this classification

Bus Network Topology bull All the nodes (file server workstations and peripherals) on a bus topology are connected by one single cable bull A bus topology consists of a main run of cable with a terminator at each end All nodes (file server workstations and peripherals) are connected to the linear cable bull Popular on LANs because they are inexpensive and easy to install

Advantages of Bus Topology bull It is Cheap easy to handle and implement bull Require less cable bull It is best suited for small networks Disadvantages of Bus Topology bull The cable length is limited This limits the number of stations that can be connected bull This network topology can perform well only for a limited number of nodes

Bus Network Topology Star Network Topology

Star Network Topology bull In a star network each node (file server workstations and peripherals) is connected to a central device called a hub bull The hub takes a signal that comes from any node and passes it along to all the other nodes in the network bull Data on a star network passes through the hub switch or concentrator before continuing to its destination bull The hub switch or concentrator manages and controls all functions of the network bull The star topology reduces the chance of network failure by connecting all of the systems to a central node Advantages of Star Topology bull Easy to manage bull Easy to locate problems (cableworkstations) bull Easier to expand than a bus or ring topology

bull Easy to install and wire bull Easy to detect faults and to remove parts Disadvantages of Star Topology bull Requires more cable length than a linear topology bull If the hub or concentrator fails nodes attached are disabled bull More expensive because of the cost of the concentrators

Ring Network Topology

bull In a ring network every device has exactly two neighbours for communication purposes bull All messages travel through a ring in the same direction bull A failure in any cable or device breaks the loop and can take down the entire network bull To implement a ring network we use the Token Ring technology bull A token or small data packet is continuously passed around the network When a device needs to transmit it reserves the token for the next trip around then attaches its data packet to it Advantage of Ring Topology bull Very orderly network where every device has access to the token and the opportunity to transmit bull Easier to Mange than a Bus Network bull Good Communication over long distances bull Handles high volume of traffic Disadvantages of Ring Topology bull The failure of a single node of the network can cause the entire network to fail bull The movement or changes made to network nodes affects the performance of the entire network

Ring Network Topology Mesh Network Topology

Mesh Network Topology

bull In this topology each node is connected to every other node in the network

bull Implementing the mesh topology is expensive and difficult bull In this type of network each node may send message to destination through multiple paths bull While the data is travelling on the Mesh Network it is automatically configured to reach the destination by taking the shortest route which means the least number of hops Advantage of Mesh Topology bull No traffic problem as there are dedicated links

bull It has multiple links so if one route is blocked then other routes can be used for data communication bull Points to point links make fault identification easy Disadvantage of Mesh Topology bull There is mesh of wiring which can be difficult to manage bull Installation is complex as each node is connected to every node bull Cabling cost is high

Tree Network Topology

bull A tree topology (hierarchical topology) can be viewed as a collection of star networks

arranged in a hierarchy

bull This tree has individual peripheral nodes which are required to transmit to and receive from one other only and are not required to act as repeaters or regenerators bull The tree topology arranges links and nodes into distinct hierarchies in order to allow greater control and easier troubleshooting bull This is particularly helpful for colleges universities and schools so that each of the connect to the big network in some way Advantages of a Tree Topology bull Point-to-point wiring for individual segments bull Supported by several hardware and software vendors bull All the computers have access to the larger and their immediate networks Disadvantages of a Tree Topology bull Overall length of each segment is limited by the type of cabling used bull If the backbone line breaks the entire segment goes down bull More difficult to configure and wire than other topologies

Hybrid topology

bull A combination of any two or more network topologies

bull A hybrid topology always accrues when two different basic network topologies are connected bull It is a mixture of above mentioned topologies Usually a central computer is attached with sub-controllers which in turn participate in a variety of topologies Advantages of a Hybrid Topology bull It is extremely flexible bull It is very reliable Disadvantages of a Hybrid Topology bull Expensive

Data Access System in LAN Two important data access systems are i) CSMA CSMACD and CSMACA ii) Token Passing

i) Carrier Sensed Multiple Access (CSMA) CSMA is a network access method used on

shared network topologies such as Ethernet to control access to the network Devices

attached to the network cable listen (carrier sense) before transmitting If the channel is

in use devices wait before transmitting MA (Multiple Access) indicates that many devices

can connect to and share the same network All devices have equal access to use the network

when it is clear Even though devices attempt to sense whether the network is in use there

is a good chance that two stations will attempt to access it at the same time On large

networks the transmission time between one end of the cable and another is enough that one

station may access the cable even though another has already just accessed it There are

two methods for avoiding these so-called collisions listed here

CSMACD (Carrier Sense Multiple AccessCollision Detection) CD (collision detection)

defines what happens when two devices sense a clear channel then attempt to transmit at

the same time A collision occurs and both devices stop transmission wait for a random

amount of time and then retransmit This is the technique used to access the 8023

Ethernet network channel This method handles collisions as they occur but if the bus is

constantly busy collisions can occur so often that performance drops drastically It is

estimated that network traffic must be less than 40 percent of the bus capacity for the

network to operate efficiently If distances are long time lags occur that may result in

inappropriate carrier sensing and hence collisions

CSMACA (Carrier Sense Multiple AccessCollision Avoidance) In CA (collision avoidance)

collisions are avoided because each node signals its intent to transmit before actually

doing so This method is not popular because it requires excessive overhead that reduces

performance

ii) Token Passing In case of token passing there is no chance for collision Here the

data are divided into frames Token is the simple frame which is the permission for the

data transmission In this system each station can send signal in turn Each station sends

signal only during its turn and sends one frame only A token passes from station to

station around the ring A station may send data when it receives the token

LAN Protocols i) Ethernet The Ethernet topology was developed at the University of Hawaii to connect computers on the various Islands It was radio based design Ethernet is one of the most

popular Computer Network or LAN technologies in use today covering more than 85 of the computer networks Ethernet system consists of three basic elements 1 The physical medium use to carry Ethernet signals between computers on the network 2 A set of rules (protocols) embedded in each Ethernet interface that will decide how multiple computers on the network will have access to the data on the medium 3 An Ethernet frame that consists of a standardized set of bits used to carry data over the system The operation of Ethernet can be described in simple terms as follows Each computer on the Ethernet Network also known as a node operates independently of all other nodes All nodes attached to an Ethernet are connected to a shared medium over which the Ethernet signals travel serially one data bit at a time To send data a station first listens to the channel and when the channel is idle the station transmits its information in the form of an Ethernet frame or packet The Ethernet rules (protocol) are defined in such a way that every node gets a fair amount of frame transmission opportunity As each Ethernet frame is sent out on the shared medium the Ethernet interfaces inside the node look at the destination address The interfaces compare the destination address of the frame with their own address The Ethernet interface with the same address as the destination address in the frame will read the entire frame and all other network interfaces will ignore the information Medium Access Control of Ethernet The set of rules which ensures that every node in an Ethernet gets a fair amount of frame transmission opportunity are called the Medium Access Control mechanism The Medium Access Control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMDCD) Ethernet Frame The heart of Ethernet system is the Ethernet Frame which is used to deliver information between the computers The frame consists of a set of bits organized into several fields These fields include address fields a data field and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact Advantages of Ethernet Ethernets major advantages are 1 It is an inexpensive way to achieve high speed LAN transmissions (10 to 100 MBs)

2 It is a proven technology that supports various writing configurations 3 It works well with a large number of LAN and micro-to-mainframe applications 4 It is easy to install Disadvantages of Ethernet The Ethernet cabling ahs the following disadvantages 1 Ethernet is not a high-level performer in high-load environments This protocol (CSMACD Carrier Sense Multiple AccessCollision Detection) can slow down dramatically if hundreds of workstations are competing for the same cabling trunk 2 Its linear bus cabling system can sometimes make it difficult to isolate problems

ii) Token Ring Token ring local area network (LAN) technology is a protocol which resides at the data link layer (DLL) of the OSI model It uses a special three-byte frame called a token that travels around the ring Token-possession grants the possessor permission to transmit on the medium Token ring frames travel completely around the loop

Initially used only in IBM computers it was eventually standardized with protocol IEEE 8025

The data transmission process goes as follows

Empty information frames are continuously circulated on the ring When a computer has a message to send it inserts a token in an empty frame (this may

consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame

The frame is then examined by each successive workstation The workstation that identifies itself to be the destination for the message copies it from the frame and changes the token back to 0

When the frame gets back to the originator it sees that the token has been changed to 0 and that the message has been copied and received It removes the message from the frame

The frame continues to circulate as an empty frame ready to be taken by a workstation when it has a message to send

The token scheme can also be used with bus topology LANs

Advantages of Token Ring

Here are Token rings most useful advantages

a It offers excellent throughput under high-load conditions

b Token Ring facilitates LAN-to-LAN mainframe connections especially for interfacing with

IBMs broader connectivity strategies

c It has built-in troubleshooting mechanisms such as beaconing and auto-reconfiguration

and may now be used with UTP cabling

d It has the most reliable protocol (token-passing) the most trouble-free configuration

(physical star) and the fastest connectivity scheme (r or 16 mbs)

Disadvantages of Token Ring

Few of the disadvantages of Token Ring are

a Token Ring is very expensive All topology components cost much more than other more

popular standards

b It is relatively proprietary Token Rings complexity is built into the hardware

components This means hat you need to choose a manufacturer and stick with it

c Engineers must have considerable expertise to manage and troubleshoot token ring

components

Data Transmission Techniques in WAN See Switching

WAN Devices i)Network Repeater A repeater connects two segments of your network cable It retimes and regenerates the signals to proper amplitudes and sends them to the other segments When talking about ethernet topology you are probably talking about using a hub as a repeater Repeaters require a small amount of time to regenerate the signal This can cause a propagation delay which can affect network communication when there are several repeaters in a row Many network architectures limit the number of repeaters that can be used in a row Repeaters work only at the physical layer of the OSI network model ii)Bridge A bridge reads the outermost section of data on the data packet to tell where the message is going It reduces the traffic on other network segments since it does not send all packets Bridges can be programmed to reject packets from particular networks Bridging occurs at the data link layer of the OSI model which means the bridge cannot read IP addresses but only the outermost hardware address of the packet In our case the bridge can read the ethernet data which gives the hardware address of the destination address not the IP address Bridges forward all broadcast messages Only a special bridge called a translation bridge will allow two networks of different architectures to be connected Bridges do not normally allow connection of networks with different architectures The hardware address is also called the MAC (media access control) address To determine the network segment a MAC address belongs to bridges use one of Transparent Bridging - They build a table of addresses (bridging table) as they receive packets If the address is not in the bridging table the packet is forwarded to all segments other than the one it came from This type of bridge is used on ethernet networks Source route bridging - The source computer provides path information inside the packet This is used on Token Ring networks iii)Network Router A router is used to route data packets between two networks It reads

the information in each packet to tell where it is going If it is destined for an

immediate network it has access to it will strip the outer packet readdress the packet

to the proper ethernet address and transmit it on that network If it is destined for

another network and must be sent to another router it will re-package the outer packet

to be received by the next router and send it to the next router The section on routing

explains the theory behind this and how routing tables are used to help determine packet

destinations Routing occurs at the network layer of the OSI model They can connect

networks with different architectures such as Token Ring and Ethernet Although they can

transform information at the data link level routers cannot transform information from

one data format such as TCPIP to another such as IPXSPX Routers do not send broadcast

packets or corrupted packets If the routing table does not indicate the proper address

of a packet the packet is discarded

iv)Brouter There is a device called a brouter which will function similar to a bridge for

network transport protocols that are not routable and will function as a router for

routable protocols It functions at the network and data link layers of the OSI network

model

v)Gateway A gateway can translate information between different network data formats or

network architectures It can translate TCPIP to AppleTalk so computers supporting TCPIP

can communicate with Apple brand computers Most gateways operate at the application layer

but can operate at the network or session layer of the OSI model Gateways will start at

the lower level and strip information until it gets to the required level and repackage the

information and work its way back toward the hardware layer of the OSI model To confuse

issues when talking about a router that is used to interface to another network the word

gateway is often used This does not mean the routing machine is a gateway as defined here

although it could be

vi)Modem A modem (modulator-demodulator) is a device that modulates an analog carrier

signal to encode digital information and also demodulates such a carrier signal to decode

the transmitted information The goal is to produce a signal that can be transmitted easily

and decoded to reproduce the original digital data Modems can be used over any means of

transmitting analog signals from light emitting diodes to radio The most familiar example

is a voice band modem that turns the digital data of a personal computer into

modulated electrical signals in the voice frequency range of a telephone channel These

signals can be transmitted over telephone lines and demodulated by another modem at the

receiver side to recover the digital data

OSI Model The Open Systems Interconnect (OSI) model has seven layers This article describes and

explains them beginning with the lowest in the hierarchy (the physical) and proceeding

to the highest (the application) The layers are stacked this way

bull Application bull Presentation bull Session bull Transport bull Network bull Data Link bull Physical

PHYSICAL LAYER

The physical layer the lowest layer of the OSI model is concerned with the transmission

and reception of the unstructured raw bit stream over a physical medium It describes the

electricaloptical mechanical and functional interfaces to the physical medium and

carries the signals for all of the higher layers It provides

bull Data encoding modifies the simple digital signal pattern (1s and 0s) used by the PC to better accommodate the characteristics of the physical medium and to aid in bit and frame synchronization It determines

o What signal state represents a binary 1 o How the receiving station knows when a bit-time starts o How the receiving station delimits a frame

bull Physical medium attachment accommodating various possibilities in the medium

o Will an external transceiver (MAU) be used to connect to the medium o How many pins do the connectors have and what is each pin used for

bull Transmission technique determines whether the encoded bits will be transmitted by baseband (digital) or broadband (analog) signaling

bull Physical medium transmission transmits bits as electrical or optical signals appropriate for the physical medium and determines

o What physical medium options can be used o How many voltsdb should be used to represent a given signal state using a

given physical medium

DATA LINK LAYER

The data link layer provides error-free transfer of data frames from one node to another

over the physical layer allowing layers above it to assume virtually error-free

transmission over the link To do this the data link layer provides

bull Link establishment and termination establishes and terminates the logical link between two nodes

bull Frame traffic control tells the transmitting node to back-off when no frame buffers are available

bull Frame sequencing transmitsreceives frames sequentially bull Frame acknowledgment providesexpects frame acknowledgments Detects and recovers

from errors that occur in the physical layer by retransmitting non-acknowledged frames and handling duplicate frame receipt

bull Frame delimiting creates and recognizes frame boundaries bull Frame error checking checks received frames for integrity bull Media access management determines when the node has the right to use the physical

medium

NETWORK LAYER

The network layer controls the operation of the subnet deciding which physical path the

data should take based on network conditions priority of service and other factors It

provides

bull Routing routes frames among networks bull Subnet traffic control routers (network layer intermediate systems) can instruct a

sending station to throttle back its frame transmission when the routers buffer fills up

bull Frame fragmentation if it determines that a downstream routers maximum transmission unit (MTU) size is less than the frame size a router can fragment a frame for transmission and re-assembly at the destination station

bull Logical-physical address mapping translates logical addresses or names into physical addresses

bull Subnet usage accounting has accounting functions to keep track of frames forwarded by subnet intermediate systems to produce billing information

TRANSPORT LAYER

The transport layer ensures that messages are delivered error-free in sequence and with

no losses or duplications It relieves the higher layer protocols from any concern with the

transfer of data between them and their peers

The size and complexity of a transport protocol depends on the type of service it can get

from the network layer For a reliable network layer with virtual circuit capability a

minimal transport layer is required If the network layer is unreliable andor only

supports datagrams the transport protocol should include extensive error detection and

recovery

The transport layer provides

bull Message segmentation accepts a message from the (session) layer above it splits the message into smaller units (if not already small enough) and passes the smaller units down to the network layer The transport layer at the destination station reassembles the message

bull Message acknowledgment provides reliable end-to-end message delivery with acknowledgments

bull Message traffic control tells the transmitting station to back-off when no message buffers are available

bull Session multiplexing multiplexes several message streams or sessions onto one logical link and keeps track of which messages belong to which sessions (see session layer)

Typically the transport layer can accept relatively large messages but there are strict

message size limits imposed by the network (or lower) layer Consequently the transport

layer must break up the messages into smaller units or frames prepending a header to each

frame

The transport layer header information must then include control information such as

message start and message end flags to enable the transport layer on the other end to

recognize message boundaries In addition if the lower layers do not maintain sequence

the transport header must contain sequence information to enable the transport layer on the

receiving end to get the pieces back together in the right order before handing the

received message up to the layer above

SESSION LAYER

The session layer allows session establishment between processes running on different

stations It provides

bull Session establishment maintenance and termination allows two application processes on different machines to establish use and terminate a connection called a session

bull Session support performs the functions that allow these processes to communicate over the network performing security name recognition logging and so on

PRESENTATION LAYER

The presentation layer formats the data to be presented to the application layer It can be

viewed as the translator for the network This layer may translate data from a format used

by the application layer into a common format at the sending station then translate the

common format to a format known to the application layer at the receiving station

The presentation layer provides

bull Character code translation for example ASCII to EBCDIC bull Data conversion bit order CR-CRLF integer-floating point and so on bull Data compression reduces the number of bits that need to be transmitted on the

network bull Data encryption encrypt data for security purposes For example password

encryption

APPLICATION LAYER

The application layer serves as the window for users and application processes to access

network services This layer contains a variety of commonly needed functions

bull Resource sharing and device redirection bull Remote file access bull Remote printer access bull Inter-process communication bull Network management bull Directory services bull Electronic messaging (such as mail) bull Network virtual terminals

ISDN Integrated Services Digital Network is a telephone system network It is a wide area

network becoming widely available Prior to the ISDN the phone system was viewed as a way

to transport voice with some special services available for data The key feature of the

ISDN is that it integrates speech and data on the same lines adding features that were not

available in the classic telephone system ISDN is a circuit -switched telephone network system that also provides access to packet switched networks designed to allow digital transmission of voice and data over ordinary telephone copper wires resulting in better voice quality thanmiddot an analog phone It offers circuit-switched connections (for either voice or data) and packet-switched connections (for data) in increments of 64 Kbits Another major market application is Internet access where ISDN typically provides a maximum of 128 Kbits in both upstream and downstream directions (which can be considered to be broadband speed since it exceeds the narrowband speeds of standard analog 56k telephone lines)

The principle of ISDN

The ISDN is supported by a wide range of voice and non-voice applications of the same

network It provides a range of servicesmiddot using a limited set of connections and

multipurpose user-network interface arrangements

ISDN supports a variety of applications that include both switched and non-switched

connections The switched connections Include both circuit and packet switched

connections

As far as possible new services introduced into an ISDN should be arranged to be

compatible with the 64 Kbps switched digital connections

A layered protocol structure should be used for the specification of access to an ISDN

This is the same as the OSI reference model The standards which have already been

developed for OSI applications such as X25 can be used for ISDN

ISDNs may be implemented in a variety of configurations

ISDN Services

The purpose of the ISDN is to provide fully integrated digital services to users These

services fall into categories- better services teleservices and supplementary services

1 Bearer Services Bearer services provide the means to transfer information (voice data

and video) between users without the network manipulating the content of that information

The network does not need to process the information and therefore does not change the

content Bearer services belong to the first three layers of the OSI model and are well

defined in the ISDN standard They can be provided using circuit-switched packet-switched

frame-switched or cell-switched networks

2 Teleservices In teleservices the network may change or process the contents of the

data These services correspond to layers 4-7 of the OSI model Teleservices relay on the

facilities of the bearer services and are designed to accommodate complex user needs

without the user having to be aware of the details of the process Teleservices include

telephony teletex telefax videotex telex and teleconferencing Although the ISDN

defines these services by name they have not yet become standards

3 Supplementary Service Supplementary services are those services that provide additional

functionality to the bearer services and teleservices Examples of these services are

reverse charging call waiting and message handling all familiar from todays telephone

company services

Networking Questions

A) Answer the following questions- 1) What is computer network Write its importance

2) What are the difference between Asynchronous transmission and Synchronous Transmission

3) What is LAN MAN WAN

4) Define Topology

5) What are the advantage and disadvantage of Ring Topology

6) What are the advantage and disadvantage of Tree topology

7) Write short notes on Ethernet and Token Ring

8) Define ISDN

9) Describe Datalink layer and Transport layer

10) What is Firewall

B) MCQ questions and Answer- 1) The full form of CSMACD-

a)Carrier sense multiple access with collision detection

b)Carrier system multiple access with collision device

c)Cancel system multiple access with collision device

d) none of these

Ans-a

2) X25_________protocol

a) Packet switching b)CSMACD c)Message switching d)All of these

Ans-a

3) Connectionless protocol is-

a)TCP b)UDP c)ARP d)RARP

Ans-b

4) Required protocol of Transport layer in TCPIP model-

a)ARPRARP b)TCPUDP c)ICMPUDP d)None of these

5) When a wire or cable transport a signal in a time in network system is called-

a)Broadband network b)Baseband network c)Client server d)None of these

Ans-a

6) Digital signal is formed with

a) Electromagnetive wave b)0 and 1 c)voice and data d)none of these

Ans-b

7) Example of half duplex-

a)Telephone b) Radio c)walkie talkie d)television

Ans-c

8) The full form of NIC-

a)Network interface card b)network installation card c)None of these d)All

Ans-a

9) Start bit and stop bit is used in -

a) Asynchronous transmission b) Syschronous transmission c) Client server d) None of these

Ans-a

10) When each computer work server as well as client in network system is called-

a)LAN b) MAN C) Client server d) Peer to Peer

Ans-d

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Database Management SystemDatabase Management SystemDatabase Management SystemDatabase Management System Data Data হল কান িবষয় ব বা বি সপিক ত অথ হীন অসংগিঠত াথিমক সংখা অথবা শ$ যার িনিদ ( প)িতেত ি+য়াকরণ বা িবে-ষেণর (Processing) পর সসংগিঠত অথ পণ হয় Information ববহােরর অনপয াথিমক ডটািল ি+য়াকরণ বা িবে-ষেণর মাধেম য অথ পণ সসংগিঠত ও ববহােরর উপেযাগী িহসােব পিরণত হয় তােক Information বেল Data Processing Data ক ইনফেম শন এ পিরণত করার প)িতেক Data Processing বেল Data ও Information এর পাথ ক

Data Information 1H Data হল কান বি ব ইতািদ সপিক ত অসংগিঠত াথিমক তথ

1H ইনফেম শন হল ি+য়াকরণ বা Process করার পর সগিঠত এবং অথ পণ তথ

2H Data হল ি+য়াকরণ বা িবে-ষেণর পেব র Jপ 2H ইনফেম শন হল ি+য়াকরণ বা িবে-ষেণর পরবত ী Jপ

3H Data সংLহ অেনক সময় পিরMম ও বয় সােপN 3H ইনফরেমশন Oতরীর NেP অেনক কম সময় পিরMম ও বয় হয়

Database Database হল পারRপিরক সপক য তথ যখােন িবিধব) (Structured) ববVার মাধেম সসংহত ভােব ও Xত তথ সংরিNত করা যায়Database এ সম Data বা তথেক এক বা একািধক টিবেলর মেধ সংরিNত করা হয়

Database Management System Database Management System বা DBMS হেলা একছ Programme এর সমাহার যখােন পারRপিরক সপক য তথেক িবিধব) ববVার মাধেম সসংহত ভােব ও Xত সংরিNত করা হয় এছাড়াও তেথর নবীকরণ (Update) িবেয়াজন (Delete) ইতািদ েয়াজন অনসাের িনিদ ( তেথর পয েবNণ খবই Xততার সেc সপাদন করা যায়

DBMS এর েয়াগ 1H বাংিকংেয়র NেP বত মােন ডটােবস িসেdেমর ভত ববহার লN করা যায় 2H এয়ারলাইনস ও রলওেয় িরজােভ শন এর NেP ডটােবস িসেdম ববeত হয় 3H আিথ ক িহসাব -িনকােশর NেPও ডটােবস িসেdেমর ভত ববহার লN করা যায় DBMS এর সিবধা 1H ডটােবস িসেdেম তেথর বাhল জিনত সমসা (Data Redundancy) িনয়jণ করা যায় 2H তেথর অসcিত (Data Inconsistency) ডাটােবজ িসেdম এ দর করা সkব 3H তেথর অখlতা (Data Integrity) এবং তেথর মৗিলকn (Data Independency) রNা করা যায় 4H ডটােবস িসেdেম বাকআপ প)িতর মাধেম ডটা পনp)ার সkব DBMS এর অসিবধা 1H ডটােবস িসেdেম সম ডটা কqrীয়ভােব িনয়িjত হওয়ায় কান sিট দখা িদেল সাধারণ ববহারকারী সংেশাধন করেত পােরনা 2H ডটােবস িসেdেম য সম সফটওয়ার ইিtিনয়ার ডটােবস অাডিমিনেuটর ডটােবস িডজাইনার ডটােবস অপােরটর েতকেক কােজ দN হেত হয় 3H ডটােবস িসেdম Vাপন ও রNণােবNণ যেথ( বয়বhল 4H ডটােবস িসেdম তলনামলকভােব অেনক জিটল ি+য়া ডটা িডকশনাির (Data Dictionary) ডটা িডকশনাির এমন একিট মটােডটার সংLহয ফাইল যখােন i) ডটােবেসর ডটা সপািকত িবিভv তথ(যমন ডটার অথ ৬টার উৎপিy অন ডটার সেc সপক জটার বাবহার ডটার ধরন ও আকার ডটার ফরমযাট ইতািদ) অবVান কের ii) ডটােবেসর সম ফাইলিলর তািলকা সংরিNত থােক iii) িতিট ফাইেলর রকত সংখা এবং িফz বা ডটা পেদর নাম এবং ধন সংরিNত থােক iv) +মানসাের িনিদ ( সিচ ও িনয়ম অনসাের ফাইলিলর পিরচায় সিচপP আকাের রাখা গােক v) ডটােবেসর টাবেলর NেP িবিভv তথ (যমন-টিবেলর নাম টিবেলর ওনার (Owner) বা মািলক কখন টিবলিট


Oতির করা হয়েছ এবং শষ কেব টিবলিট অাকেসস করা হেয়েছ টিবলিটর uাকচার বা গঠন ইতািদ) সংরিNত থােক vi) ডটােবেসর অবেজিলর ইনেড (Index) কেqটস (Constraints) আকেসস রাইট (Access Right) িভফqট মান (Default Value) ইতািদ সংরিNত থােক তাই ডটা িডকশনাির কতপেN ভটােবেসর মটােডটা য ফাইেল সিচত থােক তােক বােঝায় তেব ডটা িভকশনািরেত কত ডটা থােক না এবং ডটা িডকশনাির ছাড়া DBMS ডটােবস থেক ডটা অাকেসস করেত পাের না DBMS-এ ডটা িডকশনাির লকািয়ত (Hidden) অবVায় রাখা হয় িনরাপyার কারেণ তেব ডটােবেসর pnপণ ববহারকারী যমন-ডটােবস আাডিমিনেuটর (DBA) অািেকশন াLামার ডটা মােনজার ইতািদ শাসক ডটা িডকশনাির ববহার করেত পাের মটােডটা (Metadata) মটােডটা হল ডটা অাবাউট ডটা (Data About Data) অথ াৎ কােনা ডটা সপেক বণ না করার জন য ডটা ববহার করা হয় তােক মটােডটা বেল ডটােবস িসেdেম ডটা িডকশনাির (Data Dictionary)-রমেধ মটােডটা সিত থােক মটােডটার মাধেম কােনা ডটােবস অবেজের যসব তথিল সংরিNত থােক সিল হল i অবেজিটর ওনার (Owner) বা মািলক এবং গঠন iiH অবেজের ডটাটাইপ ও আকার iiiH অবেজিট কখন Oতির করা হেয়েছ ivH শষ কখন অবেজিট ববহার করা হেয়েছ vH অবেজিটর অাকেসস রাইট (Access Right) ইতািদ উদাহরেণর সাহােয মটােডটার ধারণা করা যেত পাের যমন - iH একিট টট ফাইেলর NেP তার সাইজ তার লখক কান তািরেখ Oতির এবং কান তািরেখ শষ পিরবত ন করা হেয়েছ ইতািদর িববরণ হল ওই ফাইেলর মটােডটা iiH ছিবয কােনা ফাইেলর মটােডটা হল তার সাইজ (Size) রেজািলউশন (Resolution) ইতািদ iiH আবার ওেয়বেপেজর NেP মটােডটা হলেপজিট কান ভাষায় লখা হেয়েছ ববeত টলস পজিটর িবষয়ব ইতািদ ডটােবস িমা (Schema) ও ইনdা (Instance) িমা (Schema) কােনা ডটােবেসর বা টিবেলর গঠন য প)িতর মাধেম িনধ ািরত হয় তােক ডটােবস িমা (Schema) বেল অথ াৎ ডটােবস িমার মাধেম টিবেলর নাম কলাম বা অািিবউের নাম এবং তােদর ডটা টাইপ উেখ করা হয় ইটা (Instance) ডটােবস িসেdেম কােনা িনিদ ( মহেত া ডটার সমL িচPিটেক ওই মহেত র ডটােবস ইটা বেল সমেয়র সেc সেc ডটােবস ইটা পিরবিত ত হেত পাের DBA কী DBA বা ডটােবস অাডিমিনেuটর-এর কাজিল লখাে

Database Administrator (DBA) য বি DBMS বা ডটােবস মােনজেমqট িসেdেমর সমL ডটােবস বা সপিক ত সমL ােLামিলেক কqrীয়ভােব Pণ কের তােক DBA বা ডটােবস অাডিমিনেuটর (Database Administrator ) বেল DBA-এর কাজ (Function)িল হল-- (i) DBA ডটােবস িসেdেমর িমা বা গঠন বণ না কের (ii) ডটােবস ববহার করার NেP িবিভv ববহারকারীেক অনমিত দান কের (iii) ডটােবস িসেdেমর ডটার Oবধতা ও িনরাপy রNা কের (iv) ডটা বাকআপ (Back up) ডটার আপেডশন (Updation) িডে য়ােজনীয় জায়গা ফাকা করা ইতািদ িবিভv pnপণ কাজ সপাদন কের (v) ডটােবস িসেdেমর জন য়ােজনীয় সফটওয়ার ও হাড ওয়ার িনব াচন করা

DBMS এর 3 Schema Architecture ডটােবেসর গঠন জিটল কিতর হওয়ায় দN ডটােবস ােLামারগণ ডটােবস থেক ডটা দশ েনর NেP সাধারণ ববহারকারীেদর থেক িবিভv িবমত েরর মাধেম ডটােবেসর মল গঠনেক আড়াল কের রােখন ডটােবস িমার িবমত র িতন ভােগ িবভ-

aH িফিজকাল লেভল িমা (Physical Levকত পিরমাণ জায়গা বা Memory লাগেব তা িনধ ারণ কের এই িমার মাধেম ভৗত ের ডটােবস িডজাইন করা হয় সাধারণ ববহারকারীরা এই র অাকেসস বা ববহার করেত পাের না সাধারণত ডটােবস িডজাইনাপিরচালক িমার এই ের কাজ করেত সNমbH লিজকাল লেভল িমা (Logical Level Schema) সংরিNত dার টাইপ কীJপ হেব এবং ডটােবেস সংরিNত রকেড র পারRপিরক িরেলশন হেব তা িনধ ারণ করা হয় সাধারণত ডটােবস অাডিমিনেuটর এই ের কাজ কের ডটােবেসর ভৗত গঠন এই ের লকানাে (Hidden) থােক cH এটারনাল বা িভউ লেভল িমা (External or View Level Schema) ডটােবেসর সেc সপক (interaction) ও যাবণ না এই ের লকােনা(Hidden) থােক Data Model ডটা মেডল(Data Model) এমন একিট িবষয়এর মাধেম ডটােবেসর সম ডটািল িনেজেদরসংরিNত হেব কীভােব িনয়িjত হেব তা আডটা মেডল িবিভv কার হেত পাের যমন

Entity Relationship Model এনিটিট িরেলশনিশপ মেডল হল কতকিলসপেক র (Relationship) িচিPত Jপ যা বাব পিরিVিতেক (Real World) সqদর approach মেন চেল এনিটিট িরেলশনিশপ মেডেলর pnপণ উপাদানিল

(Physical Level Schema) এই ধরেনর িমা ডটােবেস ডটা dার বা সংরNেণর জন লাগেব তা িনধ ারণ কের এই িমার মাধেম ভৗত ের ডটােবস িডজাইন করা হয়

সাধারণ ববহারকারীরা এই র অাকেসস বা ববহার করেত পাের না সাধারণত ডটােবস িডজাইনাপিরচালক িমার এই ের কাজ করেত সNম

(Logical Level Schema) যৗিক বা লিজকাল লেভল িমা েরর মাধেম ডটােবেস সংরিNত dার টাইপ কীJপ হেব এবং ডটােবেস সংরিNত রকেড র পারRপিরক িরেলশন হেব তা িনধ ারণ করা হয় সাধারণত ডটােবস অাডিমিনেuটর এই ের কাজ কের ডটােবেসর ভৗত গঠন এই ের

(External or View Level Schema) িমার এই ের সাধারণ ববহারকারী ও যাগােযাগ গেড় তলেত সNম হেলও িমার ভৗত গঠন ও যৗিক েরর

িবষয় বা ধারণা যার মাধেম ডটােবেসর uাকচার বািনেজেদর মেধ কীভােব য থাকেব কীভােব েসসআেলািচত থােক

যমন-

কতকিল মল ধারণাগত িবষয় বা ব বা অবেজ (Entity) ডটােবস Oতির করেত ববeত হয় এনিটিট িরেলশনিশপ ও িনখতভােব ডটােবেস উপVাপন করা যায় এই

উপাদানিল হল -


এই ধরেনর িমা ডটােবেস ডটা dার বা সংরNেণর জন লাগেব তা িনধ ারণ কের এই িমার মাধেম ভৗত ের ডটােবস িডজাইন করা হয়

সাধারণ ববহারকারীরা এই র অাকেসস বা ববহার করেত পাের না সাধারণত ডটােবস িডজাইনার িসেdম

যৗিক বা লিজকাল লেভল িমা েরর মাধেম ডটােবেস সংরিNত dার টাইপ কীJপ হেব এবং ডটােবেস সংরিNত রকেড র পারRপিরক িরেলশন (Relation) বা সপক কী হেব তা িনধ ারণ করা হয় সাধারণত ডটােবস অাডিমিনেuটর এই ের কাজ কের ডটােবেসর ভৗত গঠন এই ের

িমার এই ের সাধারণ ববহারকারী গ গেড় তলেত সNম হেলও িমার ভৗত গঠন ও যৗিক েরর

বা কাঠামােক বণ না করা হয় েসস হেব কীভােব

(Entity) এবং তােদর মেধ িরেলশনিশপ মেডেলর মাধেম এই মেডলিট Top-Down

এনিটিট (Entity) এনিটিট হল Entity-relationship িচিত করা হয় এবং অন কান ব বা ঘটনা

যমন- iH কাপািনর NেP কম চাির (Employee) েতেকই এক-একিট এনিটিট iiH িবদালেয়রেNেP ছাPছাPী (Students) েতকিট এনিটিট (Entity)-ক িচ করার তjভােব িচিত করা যায় যমন-িবদালেয়ররাল নiexclর (Roll NoH) নাম (Name) িঠকানাএনিটিট সট (Entity Set) একই ধরেনরতািলকােক এনিটিট সট (Entity Set) বেলিঠকানা (Address) Phone Number DesignationiiH িবদালেয়র সম ছাPছাPীেদর (Students) (Class) ইতািদ িনেয় এনিটিট সট অািিবউট (Attribute) ডটােবেসর িতিটসেটর অািিবউট (Attribute) বেল যমননiexclর (Roll NoH) নাম (Name) িঠকানা (Address) ইতািদ iiH হাসপাতােলর ডাার (Doctor) এনিটিটফান নiexclর (Phone NoH) Rপশালাইেজশন

এনিটিট-র িবিভv কার অািিবউট থােকiH িসপল অািিবউট (Simple Attribute) অািিবউট (Simple Attribute) বেল যমনiiH কেপািসট অািিবউট (Composite Attribute) কেপািসট অািিবউট (Composite Attribute) Name ও Surname- এ ভাগ করা যায় iiH িসcল ভালড অািিবউট (Single Valuহয় তােদর িসcল ভালড অািিবউট (Single Valued Attribute)যমন ndash Student এনিটিটর রাল নiexclর (Roll NoH) ivH মালিটভালড অািিবউট (Multivalued Atribute) একািধক হয় তােদর মালিটভালড অািিবউট(Phone NoH) অািিবউেটর মান ছাP বা িরেলশনিশপ (Relationship) ডটােবেসVাপনেক িরেলশনিশপ (Relationship) বেল েতক এনিটিটর যএনিটিট সট থেক িনিদ ( এনিটিট ক পপকভােবসপক বা িরেলশনিশপ Vাপন করেত পাের

relationship মেডেলর ধান ধারণাগত িবষয় বা বঘটনা থেক সপণ পথক ভােব সনা করা যায়

(Employee) িডপাট েমqট(Department) কাdমার বা

(Students) িশNক (Teachers) ইতািদ েতেক এক-একিটকরার জন একািধক Oবিশ( থােক এবং িকছ Oবিশে(র

িবদালেয়র ছাPছাPী (Students) এই এনিটিট(Entity) িঠকানা (Address) Mিণ (Class) মাক স (Marks)

ধরেনর এবং একই Oবিশে(র একািধক এনিটিট িনেয় গিঠতবেল যমন-iH কাপািনর সম কম চারীেদর নাম (EmployeeDesignation বতন (Salary) ইতািদ মান িনেয় গিঠত

(Students) রাল নiexclর (Roll NoH) নাম (Name) িঠকানা

িতিট এনিটিট সেটর য িনজ Oবিশ( থােক তােদরযমন-iH িবদালেয়র ছাPছাPী বা Students এনিটিটর অািিবউটিল হল

(Address) ফান নiexclর (Phone NoH) Mিণ (Class)

এনিটিট-র অািিবউটিল হল আই িড (ID) নাম (Name)Rপশালাইেজশন (Specialization) ইতািদ

থােক - (Simple Attribute) সাধারণত য অািিবউটিল আর িবভ

যমন-Student এনিটিট-র রাল নiexclর (Roll NoH) (Composite Attribute) য সম অািিবউট ভেঙ ফলা বা

(Composite Attribute) বেল যমন-Student এনিটিটর নাম (Name)

(Single Valued Attribute) এনিটিট র স সম অািিবউেট(Single Valued Attribute) বেল (Roll NoH) অািিবউেটর NেP েতক ছাPবা ছাPীর

(Multivalued Atribute) িনিদ ( এনিটিট র NেP স-সমঅািিবউট (Multivalued Aftribute) বেল যমন-Student

ছাPীেদর NেP একািধক হেত পাের

ডটােবেস অবিVত একািধক এনিটিট-র মেধ পারRপিরক বেল েতক এনিটিটর য অািিবউটিটর মান তj

পপকভােব িচিত করা যায়) তার মাধেম একািধক পাের


ব যার currenারা অবেজেক

বা yenােয়qট (Customer)

একিট এনিটিট Oবিশে(র মাধেম এনিটিট ক

(Entity) র উেখেযাগ Oবিশ( হল (Marks) ইতািদ

গিঠত সট বা িলd বা (Employee Name) ID গিঠত এনিটিট সট

িঠকানা (Address) Mিণ

তােদর ওই এনিটিট বা এনিটিট এনিটিটর অািিবউটিল হল রাল

(Class) মাক স (Marks)

(Name) িঠকানা (Address)

িবভ করা যায়না তােদর িসপল (Roll NoH)

বা িবভ করা যায় তােদর Name) অািিবউটিট First

অািিবউেটর মান brvbarধমাP একিটই

ছাPীর একিট মানই হয় সম অািিবউেটর মান Student এনিটিট র ফান নiexclর

সপক (Association) তj থােক (যার মাধেম এনিটিট িনেজেদর মেধ

যমন - iH কােনা কাপািনর কম চারী (Employee) িরেলশনিশপ iiH হাসপাতােলর ডাার (Doctor) িবদালেয়র ছাPছাPী (Student) ও িশNক এনিটিট িরেলশনিশপ ডায়াLাম (Entity-Relationship Diagram or ER Diagram)য ডায়াLােমর মাধেম সমL ডটােবেসর এনিটিটডটােবসিটর সামিLক গঠন বণ না করা যায়

Relationship Diagram or ER Diagram)

উদাহরণ িবদালেয়র িশNক (Teacher)

িবিভv কার কী (Types of Key) িরেলশনাল ডটােবস মেডেল কী (Key) হলঅািিবউট বা িফল যার বা যােদর মাধেমযায় যমন -STUDENT টিবেলর (Roll Name Class Phone Marksিরেলশনাল ডটা মেডেল িবিভv ধরেনর কী সপার-কী (Super-key) সপার-কী (Superঅািিবউেটর সমি( যার currenারা ঐ টিবেলর যেকােনা রকড

STUDENT টিবেলর Super-key হেলা - iH _S reg vH _S id S class viH S

(Employee) ও িডপাট েমqট (Department) এনিটিট(Doctor) ও রাগী (Patient) এর মেধ সপক বা

িশNক (Teacher) এর মেধ সপক বা িরেলশনিশপ

Relationship Diagram or ER Diagram) এনিটিট-িলর মেধ সপক Vাপন বা িরেলশনিশেপযায় তােক এনিটিট িরেলশনিশপ ডায়াLাম বা ই আর

Relationship Diagram or ER Diagram) বেল এই ডায়াLাম Oতিরেত ববeত িচ বা তীক

(Teacher) ও ছাPছাPীর (Student) এনিটিট িরেলশনিশপ ডায়া

হল কােনা িনিদ ( িরেলশন বা এনিটিট-র বা টিবেলরমাধেম ওই িরেলশেনর বা টিবেলর কােনা টাপল (Tuple)

(Roll Name Class Phone Marks অািিবউটিলরকী ববeত হয় সিল হল ndash

(Super-key) হল িনিদ ( ডটােবস িরেলশন বা টিবেলরঅািিবউেটর সমি( যার currenারা ঐ টিবেলর যেকােনা রকড ক তjভােব (Lniquely) শনাy

iH _ S id iiH _ _S id S nameH iiiH _S_ _S name S ph _S class ইতািদ


এনিটিট র মেধ সপক বা বা িরেলশনিশপ iiiH

িরেলশনিশেপর িচP তেল ধের আর ডায়াLাম (Entity

তীকিল হেলা ndash

ডায়াLাম হল-

টিবেলর এক বা একািধক (Tuple) বা রকড েক সনা করা

অািিবউটিলর মেধ কী (Key) হল Roll

টিবেলর এক বা একািধক িফz বা শনাy (Identify) করা যায়

_ _ name S reg S add ivH


কািlেডট-কী Candidate-key িরেলশনাল ডটােবস িসেdেম এক বা একািধক সপার-কী (Super-key)-িলর মেধ য সম সপার-কী -ক আর ছাটা করা বা ভাঙা যায় না এবং ছাটা করেলও সই ছাটা ছাটা অংশ ( কতপেN এক বা একািধক অািিবউট) currenারা ডটােবস টিবেলর কােনা রকড েক yordfভােব (Uniquely)িচিত করা যায় না তােক ওই টিবেলর কািlেডট-কী (Candidate-key) বেল অতএব দy সপার-কী-িলর মেধ i iv ও vi হল কািlেডট-কী (Candidate-key) াইমাির-কী (Primary-key) কােনা িরেলশনাল ডটােবস িসেdেম কানা িরেলশেনরেটিবেলর কািlেডট-কী-িলর মেধ সবােচেয় Nr কী যার currenারা ওই িরেলশন বা টিবেলর য-কানা টাপল (Tuple) বা রকড েক তjভােব (Uniquely) িচিত করা যায় তােক ওই িরেলশন বা টিবেলর াইমাির -কী (Primary-key) বেল টিবেল এই Key-এর মান সবসময় তj (Distinct) এবং কখনাই ফাকা (NULL) হেত পাের না উদাহরণ দy STUDENT টিবেলর 3িট কািlেডট-কী অবVান কের - _ iH S id _ _iiH (S reg iiiH S name _ _ S ph S class I এর মেধ _ S id হল STUDENT টিবেলর াইমাির-কী [তেব এখােন _ S reg ও Primary-key

িহেসেব ববহার করা যত] াইমারী কী এর Oবিশ( ( Characteristics of Primary Key) iH কানা িরেলশন বা ডটােবস টিবেল brvbarধমাP একিটই াইমাির-কী থােক iH াইমাির-কী য অািিবউেটর মান কখনােই ফাকা বা শন হয় না iiH াইমাির-কী অািিবউেটর মান ডিেকট হওয়া থেক িতরাধ কের অshyটারেনট -কী (Alternate-key) কানা িরেলশন বা ডটােবস টিবেলর কািlেডট-কী-িলর মেধ য-কানা একিটেক াইমাির-কী িহেসেব বেছ নওয়ার পর বািক য কী বা কী-সটিল পেড় থােক তােক অshyটারেনট-কী (Alternate-key) বেল উদাহরণ দy STUDENT টিবেলর 3িট কািlেডট-কী অবVান কের - _ _ iH S id iiH S reg iiiH

_ _ _ (S name S ph S class এর মেধ _ (S id -ক াইমাির-কী িহেসেব বেছ িনেল বািক (ii) ও (iii) কী সট পেড় থােক এিলই STUDENT টিবেলর অshyটারেনট -কী (Alternate Key) কপািজট-কী (Composite-key) ডটােবস িসেdেম কখনও কখনও কানা িরেলশন বা টিবল বা এনিটিট-র অেনক সময় তj িফz বা অযািিবউট থােক না সেNেP একািধক িফz বা অািিবউট িমিলত হেয় ওই টিবেলর াইমাির-কী (Primary-kev) িহেসেব কাজ কের তখন ওই একািধক িফেzর সটেক কপািজট-কী (Composite-key) বেল উদাহরণ ধরা যাক Employee Dept Salary নােম িতনিট টিবল আেছ

_ _ _ _ _iH Employee (E id E name E city E designation Dept id) _ _ _iiH Dept (Dept id Dept name Dept location)

_ _iiiH Salary(E id Dept id amount doj)H ওপেরর iH নং টিবেলর াইমাির-কী _E id এবং iiH নং টিবেলর াইমাির-কী Dept id িক iii নং টিবেলর কানা তj িফz বা অিিবউট নই _ _ E id Dept id কী-সট Salary টিবেলর াইমাির-কী িহেসেব কাজ কের শিশালী (Strong) এবং দব ল (Weak) এনিটিট ডটােবেসর য সম এনিটিট-র অািিবউট থেক িনিদ ( াইমাির-কী খেজ পাওয়া যায়H তােক শীিশালী এনিটিট বেল যমন-Student (RollName Sex City Mark) এনিটিট-র াইমাির-কী Roll য-সম এনিটিট-র অািিবউট থেক িনিদ ( াইমাির-কী খেজ পাওয়া যায় না তােক দব ল এনটািট বেল যমন-Loan

_(Loan name _Loan date) এনিটিট-র থেক াইমাির-কী পাওয়া যায় না ডটােবস কেqটস (Database Constraints) কেqটস (Contraints) িরেলশনাল ডটােবেস ডটার সিঠকতা (accuracy) িবmacrতা (Reliability) সপণ তা (Completeness) ইতািদ বজায় রাখার জন ডটা েবশ করার সময় য িনয়ম নীিত (Rules) ববহার করা হয় তােক


ডটােবস কেqটস (constraints) বেল ডটােবেস িবিভv ধরেনর কেqটস (Constraints) ববeত হয় সিল হল - (i) এনিটিট ইিqটিLিট কেqটস (Entity Integrity Constraints) িরেলশনাস ডটােবস িসেdেম এনিটিট ইিqটিLিট কেqটস হল সই সম িনয়মনীিত যার মাধেম বাঝা যায় কানা একিট টাপল (Tuple) বা রকেড র (Rccord) াইমাির কী-এর মান কখনও শন (NULL) হেত পাের না (ii) ডামন কলেqটস (Domain Constraints) িরেলশনাল ডটােবস িসেdেম ডােেমন কqপেqটস হল সই সমসত িনয়মনীিত যার মাধেম বাঝা যায় কানা ডটােবস টিবেলর িতিট িফz বা অািিবউেটর একিট িনিদ ( ভাল (Value) বা মান আেছ যা ওই অািিবউিটর মােনর সট থেক উপলdeg হয় ধরা যাক STUDENT টিবেলর Month িফেzর মান বারা মােসর নােমর য সট হয় তার মেধ থেক য-কােনা একিট হেব (iii) রফােরিয়াল ইিqটিLিট কেqটস (Referential Integrity constraints) িরেলশনাল ডটােবস িসেdম যখন দিট টিবল বা এনিটিটর মেধ সপক বা িরেলশনিশপ Vাপন করা হয় তখন রফােরিয়াল ইিplusmnিLিট কেqqটস ববহার করা হয় এই কেqটস-এর মাধেম কানা টিবেলর ফেরন কী মােনর জন অন টিবেলর াইমাির কী-এর মান িনিsup2ত করা হয় অথ াৎ থম টিবেলর াইমাির কী িফেzর মান বতীত অন কানা মান িcurrenতীয় টিবেলর ফেরন কী িফেzর মান িহেসেব গহীত হেব না তমিন Referential Integrity িনয়েমর জন থম টিবেলর কানা ডটা মেছ ফলেল বা পিরবত ন করেল িcurrenতীয় টিবেলর ডটাও মেছ যােব বা পিরবিত ত হেব এই িনয়মেক Cascading delete বা cascading update বেল

CHAPTERCHAPTERCHAPTERCHAPTER

DATABASE DATABASE DATABASE DATABASE

MANAGEMENT MANAGEMENT MANAGEMENT MANAGEMENT

SYSTEMSYSTEMSYSTEMSYSTEM

CLASS XIICLASS XIICLASS XIICLASS XII

Data Data can be defined as a representation of facts concepts or instructions in a formalized manner which

should be suitable for communication interpretation or processing by human or electronic machine

Information Information is organized or classified data which has some meaningful values for the receiver

Information is the processed data on which decisions and actions are based

Database Database is a collection of data and Management System is a set of programs to store and retrieve

those data

Database Management System A database management system (DBMS) is a software package designed to

define manipulate retrieve and manage data in a database A DBMS generally manipulates the data itself the

data format field names record structure and file structure

Database Applications

Applications where we use Database Management Systems are

Telecom There is a database to keeps track of the information regarding calls made network usage customer

details etc Without the database systems it is hard to maintain that huge amount of data that keeps updating

every millisecond

Industry Where it is a manufacturing unit warehouse or distribution centre each one needs a database to keep

the records of ins and outs For example distribution centre should keep a track of the product units that

supplied into the centre as well as the products that got delivered out from the distribution centre on each day

this is where DBMS comes into picture

Banking System For storing customer info tracking day to day credit and debit transactions generating bank

statements etc All this work has been done with the help of Database management systems

Sales To store customer information production information and invoice details

Airlines To travel though airlines we make early reservations this reservation information along with flight

schedule is stored in database

Education sector Database systems are frequently used in schools and colleges to store and retrieve the data

regarding student details staff details course details exam details payroll data attendance details fees details

etc There is a hell lot amount of inter-related data that needs to be stored and retrieved in an efficient manner

Online shopping You must be aware of the online shopping websites such as Amazon Flipkart etc These sites

store the product information your addresses and preferences credit details and provide you the relevant list of

products based on your query All this involves a Database management system

Drawbacks of File system

Data redundancy Data redundancy refers to the duplication of data let say we are managing the data of a

college where a student is enrolled for two courses the same student details in such case will be stored twice

which will take more storage than needed Data redundancy often leads to higher storage costs and poor access

time

Data inconsistency Data redundancy leads to data inconsistency lets take the same example that we have taken

above a student is enrolled for two courses and we have student address stored twice now lets say student

requests to change his address if the address is changed at one place and not on all the records then this can lead

to data inconsistency

Data Isolation Because data are scattered in various files and files may be in different formats writing new

application programs to retrieve the appropriate data is difficult

Dependency on application programs Changing files would lead to change in application programs

Data Security Data should be secured from unauthorised

be able to see the payroll details of the teachers such kind of security constraints are difficult to apply in file

processing systems

Advantage of DBMS over file system

There are several advantages of Database management system over file system Few of them are as follows

No redundant data Redundancy removed by data

improves access time

Data Consistency and Integrity As we discussed earlier t

since data normalization takes care of the data redundancy data inconsistency also been taken care of as part of

it

Data Security It is easier to apply access constraints in database systems so th

access the data Each user has a different set of access thus data is secured from the issues such as identity theft

data leaks and misuse of data

Privacy Limited access means privacy of data

Easy access to data Database systems manages data in such a way so that the data is easily accessible with fast

response times

Easy recovery Since database system keeps the backup of data it is easier to do a full recovery of data in case of

a failure

Flexible Database systems are more flexible than file processing systems

Disadvantages of DBMS

DBMS implementation cost is high compared to the file system

Complexity Database systems are complex to understand

Performance Database systems are generic making them

DBMS ndash Three Level Architecture

Because data are scattered in various files and files may be in different formats writing new

e the appropriate data is difficult

Changing files would lead to change in application programs

Data should be secured from unauthorised access for example a student in a college should not


of Database management system over file system Few of them are as follows

No redundant data Redundancy removed by data normalization No data duplication saves storage and

Data Consistency and Integrity As we discussed earlier the root cause of data inconsistency is data redundancy


Data Security It is easier to apply access constraints in database systems so that only authorized user is able to



atabase systems manages data in such a way so that the data is easily accessible with fast

keeps the backup of data it is easier to do a full recovery of data in case of

systems are more flexible than file processing systems



Performance Database systems are generic making them suitable for various applications



access for example a student in a college should not



No data duplication saves storage and

he root cause of data inconsistency is data redundancy


at only authorized user is able to




suitable for various applications

This architecture has three levels

1 External level

2 Conceptual level

3 Internal level

External level

It is also called view level The reason this level is called ldquoviewrdquo is

data from this level which is internally fetched from database with the help of conceptual and internal level

mapping

The user doesnrsquot need to know the database schema details such as data structure table defi

only concerned about data which is what returned back to the view level after it has been fetched from database

(present at the internal level)

External level is the ldquotop levelrdquo of the Three Level DBMS Architecture

Conceptual level

It is also called logical level The whole design of the database such as relationship among data schema of data

etc are described in this level

Database constraints and security are also implemented in this level of architecture This level is maintained

DBA (database administrator)

Internal level

This level is also known as physical level This level describes how the data is actually stored in the storage

devices This level is also responsible for allocating space to the data This is the lowest le

Instance and schema in DBMS

Schema Design of a database is called the schema

and view schema

For example In the following diagram we have a schema that shows the r

Course Student and Section The diagram only shows the design of the database it doesnrsquot show the data

present in those tables Schema is only a structural view(design) of a database as shown in the diagram below

The design of a database at physical level is called

described at this level

Design of database at logical level is called

this level at this level data can be described as certain types of data records gets stored in data structures

however the internal details such as implementation of data structure is hidden at this level (available at

physical level)

Design of database at view level is called

database systems

view level The reason this level is called ldquoviewrdquo is because several users can view their desired





logical level The whole design of the database such as relationship among data schema of data




Design of a database is called the schema Schema is of three types Physical schema logical schema

For example In the following diagram we have a schema that shows the relationship between three tables



design of a database at physical level is called physical schema how the data stored in blocks of storage is

Design of database at logical level is called logical schema programmers and database administrators work at

at this level data can be described as certain types of data records gets stored in data structures


level is called view schema This generally describes end user interaction with

because several users can view their desired


The user doesnrsquot need to know the database schema details such as data structure table definition etc user is



Database constraints and security are also implemented in this level of architecture This level is maintained by


devices This level is also responsible for allocating space to the data This is the lowest level of the architecture

Schema is of three types Physical schema logical schema

elationship between three tables



physical schema how the data stored in blocks of storage is

logical schema programmers and database administrators work at



view schema This generally describes end user interaction with

Instance The data stored in database at a particular moment of time is called instance of database

schema defines the variable declarations in tab

variables at a moment of time is called the instance of that database

For example lets say we have a single table student in the database today the table has 100 records so today the

instance of the database has 100 records Lets say we are going to add another 100 records in this table by

tomorrow so the instance of database tomorrow will have 200 records in table In short at a particular moment

the data stored in database is called the ins

database

DBMS languages

Database languages are used to read update and store data in a database There are several such languages that

can be used for this purpose one of them is SQL (St

Types of DBMS languages

Data Definition Language (DDL)

DDL is used for specifying the database schema It is used for creating tables schema indexes constraints etc in

database Lets see the operations that we can perform o

To create the database instance ndash CREATE

To alter the structure of database ndash ALTER

To drop database instances ndash DROP

To delete tables in a database instance ndash

To rename database instances ndash RENAME

To drop objects from database such as tables

Data Manipulation Language (DML)

DML is used for accessing and manipulating data in a database The following operations on database comes

under DML

To read records from table(s) ndash SELECT

To insert record(s) into the table(s) ndash INS

The data stored in database at a particular moment of time is called instance of database

schema defines the variable declarations in tables that belong to a particular database the value of these



of the database has 100 records Lets say we are going to add another 100 records in this table by


the data stored in database is called the instance that changes over time when we add or delete data from the


can be used for this purpose one of them is SQL (Structured Query Language)


database Lets see the operations that we can perform on database using DDL

CREATE

ALTER

ndash TRUNCATE

RENAME

se such as tables ndash DROP


INSERT

The data stored in database at a particular moment of time is called instance of database Database

les that belong to a particular database the value of these




tance that changes over time when we add or delete data from the




Update the data in table(s) ndash UPDATE

Delete all the records from the table ndash DELETE

Data Control language (DCL)

DCL is used for granting and revoking user access on a database

To grant access to user ndash GRANT

To revoke access from user ndash REVOKE

In practical data definition language data manipulation language and data control languages are not separate

language rather they are the parts of a single database language such as SQL

Data models in DBMS

Data Model is a logical structure of Database

relationship among data constrains etc

Entity Relationship Model ndash ER Model

An Entityndashrelationship model (ER model)

is known as Entity Relationship Diagram (ER Diagram)

can later be implemented as a database The main components of E

What is an Entity Relationship Diagram (ER Diagram)

An ER diagram shows the relationship among entity sets An entity set is a group of similar entities and these

entities can have attributes In terms of DBMS an enti

showing relationship among tables and their attributes ER diagram shows the complete logical structure of a

database Lets have a look at a simple ER diagram to understand this concept

A simple ER Diagram

In the following diagram we have two entities Student and College and their relationship The relationship

between Student and College is many to one as a college can have many students however a student cannot

study in multiple colleges at the same time Student entity has attributes such as Stu_Id Stu_Name amp Stu_Addr

and College entity has attributes such as Col_ID amp Col_Name

DELETE

DCL is used for granting and revoking user access on a database ndash



is a logical structure of Database It describes the design of database to reflect


Model

relationship model (ER model) describes the structure of a database with the help of a diagram which

Entity Relationship Diagram (ER Diagram) An ER model is a design or blueprint of a database that

can later be implemented as a database The main components of E-R model are entity set and relationship set



entities can have attributes In terms of DBMS an entity is a table or attribute of a table in database so by





me time Student entity has attributes such as Stu_Id Stu_Name amp Stu_Addr



e design of database to reflect entities attributes

describes the structure of a database with the help of a diagram which

An ER model is a design or blueprint of a database that

re entity set and relationship set


ty is a table or attribute of a table in database so by





Here are the geometric shapes and their meaning in an E

Rectangle Represents Entity sets

Ellipses Attributes

Diamonds Relationship Set

Lines They link attributes to Entity Sets and Entity sets to Relationship Set

Double Ellipses Multivalued Attributes

Dashed Ellipses Derived Attributes

Double Rectangles Weak Entity Sets

Double Lines Total participation of an entity in a relationship set

Components of a ER Diagram

As shown in the above diagram an ER diagram has three main components

1 Entity

2 Attribute

3 Relationship

Here are the geometric shapes and their meaning in an E-R Diagram

hey link attributes to Entity Sets and Entity sets to Relationship Set

Multivalued Attributes

Total participation of an entity in a relationship set

hown in the above diagram an ER diagram has three main components

1 Entity

An entity is an object or component of data An entity is represented as rectangle in an ER diagram

For example In the following ER diagram we have two entities Student and College and these two entities have

many to one relationship as many students study in a single college We will read more about relationships later

for now focus on entities

Weak Entity

An entity that cannot be uniquely identified by its own attribu

is called weak entity The weak entity is represented by a double rectangle For example

be uniquely identified without knowing the bank to which the account belongs so bank acco

entity

2 Attribute

An attribute describes the property of an entity An attribute is represented as Oval in an ER diag

four types of attributes

1 Key attribute

2 Composite attribute

3 Multivalued attribute

4 Derived attribute

1 Key attribute

A key attribute can uniquely identify an entity from an entity set For example student roll number can unique

identify a student from a set of students Key attribute is represented by oval same as other attributes however

the text of key attribute is underlined


am we have two entities Student and College and these two entities have


An entity that cannot be uniquely identified by its own attributes and relies on the relationship with other entity









tes and relies on the relationship with other entity

is called weak entity The weak entity is represented by a double rectangle For example ndash a bank account cannot

be uniquely identified without knowing the bank to which the account belongs so bank account is a weak

An attribute describes the property of an entity An attribute is represented as Oval in an ER diagram There are

A key attribute can uniquely identify an entity from an entity set For example student roll number can uniquely



An attribute that is a combination of other attributes is known as composite attribute For example In student

entity the student address is a composite attribute as an address is composed of other attributes such as pin

code state country


An attribute that can hold multiple values is known as multivalued attribute It is re

ovals in an ER Diagram For example ndash A person can have more than one phone numbers so the phone number

attribute is multivalued

4 Derived attribute

A derived attribute is one whose value is dynamic and derived from another attribu

by dashed oval in an ER Diagram For example

can be derived from another attribute (Date of birth)

E-R diagram with multivalued and derived attributes

3 Relationship

A relationship is represented by diamond shape in ER diagram

are four types of relationships

1 One to One

2 One to Many

3 Many to One

4 Many to Many



An attribute that can hold multiple values is known as multivalued attribute It is represented with

A person can have more than one phone numbers so the phone number

A derived attribute is one whose value is dynamic and derived from another attribute It is represented

in an ER Diagram For example ndash Person age is a derived attribute as it changes over time and


R diagram with multivalued and derived attributes

A relationship is represented by diamond shape in ER diagram it shows the relationship among entities There



presented with double


te It is represented

Person age is a derived attribute as it changes over time and

it shows the relationship among entities There

1 One to One Relationship

When a single instance of an entity is associated with a single instance of another en

one relationship For example a person has only one passport and a passport is given to one person

2 One to Many Relationship

When a single instance of an entity is associate

one to many relationship For example ndash

many customers

3 Many to One Relationship

When more than one instances of an entity is associated with a single instance of an

many to one relationship For example ndash

in many colleges at the same time

4 Many to Many Relationship

When more than one instances of an entity is associated with more than one instances of another entity then it is

called many to many relationship For example a can be assigned to many projects and a project can be assigned

to many students

When a single instance of an entity is associated with a single instance of another entity then it is called one to


When a single instance of an entity is associated with more than one instances of another entity then it is called

ndash a customer can place many orders but a order cannot be placed by

When more than one instances of an entity is associated with a single instance of another entity then it is called

ndash many students can study in a single college but a student cannot study


d many to many relationship For example a can be assigned to many projects and a project can be assigned

tity then it is called one to


d with more than one instances of another entity then it is called

a customer can place many orders but a order cannot be placed by

other entity then it is called

many students can study in a single college but a student cannot study



Types of keys in DBMS

Primary Key ndash A primary is a column or set of columns in a table that uniquely identifies tuples (rows) in that table

Super Key ndash A super key is a set of one of more columns (attributes) to uniquely identify rows in a table

Candidate Key ndash A super key with no redundant attribute is known as candidate key

Alternate Key ndash Out of all candidate keys only one gets selected alternate or secondary keys

Composite Key ndash A key that consists of more than one attribute to uniquely identify rows (also known as records amp tuples) in a table is called composite key

Foreign Key ndash Foreign keys are the columns of a table that points to the primary key of another table They act as a cross-reference between tables

RDBMS Concepts

RDBMS stands for relational database management system A relational model can be represented as a table of

rows and columns A relational database has following major components

1 Table

2 Record or Tuple

3 Field or Column name or Attribute

4 Domain

1 Table

A table is a collection of data represented in rows and columns Each table has a name in database For

the following table ldquoSTUDENTrdquo stores the information of students in database

Table STUDENT

Student_Id Student_Name

101 Chaitanya

102 Ajeet

A primary is a column or set of columns in a table that uniquely identifies tuples (rows) in that

A super key is a set of one of more columns (attributes) to uniquely identify rows in a table

A super key with no redundant attribute is known as candidate key

Out of all candidate keys only one gets selected as primary key remaining keys are known as

A key that consists of more than one attribute to uniquely identify rows (also known as records amp tuples) in a table is called composite key

s are the columns of a table that points to the primary key of another table They act as

stands for relational database management system A relational model can be represented as a table of

and columns A relational database has following major components



Student_Name Student_Addr

Chaitanya Dayal Bagh Agra

Ajeet Delhi



as primary key remaining keys are known as

A key that consists of more than one attribute to uniquely identify rows (also known as records



A table is a collection of data represented in rows and columns Each table has a name in database For example

Student_Age

27

26

103 Rahul Gurgaon 24

104 Shubham Chennai 25

2 Record or Tuple

Each row of a table is known as record It is also known as tuple For example the following row is a record that

we have taken from the above table

102 Ajeet Delhi 26


The above table ldquoSTUDENTrdquo has four fields (or attributes) Student_Id Student_Name Student_Addr amp

Student_Age

4 Domain

A domain is a set of permitted values for an attribute in table For example a domain of month-of-year can

accept January FebruaryhellipDecember as values a domain of dates can accept all possible valid dates etc We

specify domain of attribute while creating a table

An attribute cannot accept values that are outside of their domains For example In the above table

ldquoSTUDENTrdquo the Student_Id field has integer domain so that field cannot accept values that are not integers for

example Student_Id cannot has values like ldquoFirstrdquo 1011 etc

A G Sir

Computer Networks

What is a computer Network

A network is any collection of independent computers that communicate with one another over a shared network medium A computer network is a collection of two or more connected computers When these computers are joined in a network people can share files and peripherals such as modems printers tape backup drives or CD-ROM drives When networks at multiple locations are connected using services available from phone companies people can send e-mail share links to the global Internet or conduct video conferences in real time with other remote users When a network becomes open sourced it can be managed properly with online collaboration software As companies rely on applications like electronic mail and database management for core business operations computer networking becomes increasingly more important Every network includes

bull At least two computers Server or Client workstation bull Networking Interface Cards (NIC) bull A connection medium usually a wire or cable although wireless communication

between networked computers and peripherals is also possible bull Network Operating system software such as Microsoft Windows NT or 2000 Novell

NetWare Unix and Linux

Importance of networking 1gt Resource sharing Without depending on where the computers are data can be shared

between the users

2gt High Reliability Data are stored in more than one machines because if one source is

crashed then the data can be accessed from another source So there is high

reliability

3gt Saving Money Using main frame computer system very much costly That is why network

system is used commonly

4gt Security In network system there is enough security No one can erase data easily

Some topics related to network i) Terminal Any input-output device used to send and receive data in a network

system is known as terminal Example Computers telephone Fax machine Sound box

etc

ii) Telecommunication Processors These are devices which support data transmission

and reception between terminals and computers Example Modem Multiplexers Front-

end Processor etc

iii) Telecommunication Channel and Media The media over which data are transmitted

and received are called Telecommunication Channel Example Optical Fiber Cable

Radio wave etc

iv) Computer Besides the micro computers used by the end user the computers are

used to send or processing information Various types of computers are used in

network



computers










speed






Coaxial Cable















used with a modem











Features



Limitations































bull Inexpensive


bull Easy to tap


Limitations







Features

bull Huge bandwidth



Limitations

bull Cost is high















Mbps





















Data Transmission

Parallel Serial















































































Topology










this classification

















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain









computers










speed






Coaxial Cable















used with a modem











Features



Limitations































bull Inexpensive


bull Easy to tap


Limitations







Features

bull Huge bandwidth



Limitations

bull Cost is high















Mbps





















Data Transmission

Parallel Serial















































































Topology










this classification

















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain













used with a modem











Features



Limitations































bull Inexpensive


bull Easy to tap


Limitations







Features

bull Huge bandwidth



Limitations

bull Cost is high















Mbps





















Data Transmission

Parallel Serial















































































Topology










this classification

















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain
















bull Inexpensive


bull Easy to tap


Limitations







Features

bull Huge bandwidth



Limitations

bull Cost is high















Mbps





















Data Transmission

Parallel Serial















































































Topology










this classification

















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain
















Mbps





















Data Transmission

Parallel Serial















































































Topology










this classification

















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain




















































































Topology










this classification

















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain














this classification

















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain



















Hybrid topology


























performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain































performance






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain






























popular standards




components


















model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain
























model























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain





























PHYSICAL LAYER













DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain







DATA LINK LAYER









medium

NETWORK LAYER



provides






TRANSPORT LAYER








recovery









frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain















frame







SESSION LAYER





PRESENTATION LAYER








encryption

APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































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DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain







APPLICATION LAYER















connections







ISDN Services


















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain



















company services





4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain











4) Define Topology




8) Define ISDN







d) none of these

Ans-a

2) X25_________protocol


Ans-a



Ans-b





Ans-a



Ans-b



Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain









Ans-c



Ans-a



Ans-a



Ans-d





















যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain



























যমন-























































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain




















































































those data








every millisecond




















time










processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain












processing systems







it






response times


a failure







































1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain








1 External level

2 Conceptual level

3 Internal level

External level



mapping





Conceptual level





Internal level





and view schema









physical level)


database systems











































database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain














database

DBMS languages















under DML














CREATE

ALTER

ndash TRUNCATE

RENAME



INSERT


















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain















Data models in DBMS












A simple ER Diagram





DELETE






Model


























Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain









Ellipses Attributes









1 Entity

2 Attribute

3 Relationship






1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain







1 Entity





Weak Entity




entity

2 Attribute



1 Key attribute



4 Derived attribute

1 Key attribute

























code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain










code state country





4 Derived attribute





3 Relationship



1 One to One

2 One to Many

3 Many to One

4 Many to Many























many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain













many customers








to many students
























RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain














RDBMS Concepts



1 Table

2 Record or Tuple


4 Domain

1 Table



Table STUDENT


101 Chaitanya

102 Ajeet













Ajeet Delhi








Student_Age

27

26



2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain









2 Record or Tuple



102 Ajeet Delhi 26



Student_Age

4 Domain







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