lec-1 introduction to database systems

7/28/2019 Lec-1 Introduction to Database Systems

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Definitions:Data: facts that can be recorded and that have implicitmeaning

Database: Collection of related data

Ex. the names, telephone numbers and addresses of allthe people you know

Database Management System: A computerized record-keeping system


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What is a Database?Database is shared, integrated computer structurehousing related data:

End user data (raw data)Metadata (data about data, it contains datacharacteristics and relationships

Shared collection of logically related data (and adescription of this data), designed to meet theinformation needs of an organization.


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An Example Database


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The Product Table


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DatabasesLibrary cataloguesMedical recordsBank accountsStock market dataPersonnel systemsProduct catalogues

Telephone directories

Train timetables Airline bookingsCredit card detailsStudent recordsCustomer historiesStock market prices

Discussion boardsand so on


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File TerminologyData

Raw FactsField/Attribute

Group of characters with specific meaningRecord/Tuple

Logically connected fields that describe a person,place, or thing

FileCollection of related records


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Disadvantages of Flat File SystemsNo centralized control.Data Redundancy

Data Inconsistency Data can not be sharedStandards can not be enforced

Security issuesIntegrity can not be maintainedData dependence


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Data Redundancy Different and conflicting versions of same dataResults of uncontrolled data redundancy

Data anomaliesModificationInsertion

DeletionData inconsistency

Lack of data integrity

Drawback of file system


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DBMS A software system that enables users todefine, create, and maintain the database and

that provides controlled access to thisdatabase.

The examples of DBMS are MS-ACCESS,

ORACLE, SQL SERVER etc.


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Why a DBMS?The reasons for that are, a DBMS is capable of

1. Providing data independence and efficient access of data.

2. Reducing the application development time.3. Providing Data integrity and security.4. Uniform data administration


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Importance of DBMS

Makes data management more efficient and effective Query language allows quick answers to ad hoc

queries Provides better access to more and better-managed

data Promotes integrated view of organizations

operations Reduces the probability of inconsistent data


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Why Study Databases?Databases are usefulMany computing applications deal with largeamounts of information

Database systems give a set of tools for storing,searching and managing this information


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Why and When Do We NeedDBMS?

A large amount of data,

Concurrent access by many users,Fast access,Consistent data update,Role-based security,

Robust against hardware failures and OS crashes.


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Advantages of DBMSCentralized control.No Data Redundancy

Data Consistency Data can be sharedStandards can be enforced

Security can be enforcedIntegrity can be maintainedData independence can be provided

Backup and Recovery


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Advantages of DBMSData Independence : Application program should be as independentas possible from details of data representation and storage.

Efficient Data Access : DBMS uses sophisticated techniques to storeand retrieve data efficiently. E.g. hashing, indexing.

Data Integrity and Security : DBMS enforce data integrity on the data(some constraints on data) e.g. employee number cannot bealphanumeric. Security means password protection and access levels.


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Data Administration : means organizing the database, authorizingaccess to database, managing security.

Concurrent access and crash recovery : multiple user can accessdata and DBMS protects data from system failures.

Reduced application development time : DBMS provides importantfunctions that are common to applications accessing data.

Advantages of DBMS


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Disadvantages of DBMS High startup cost (time and effort)Relatively high maintenanceCentralization increases vulnerability.SophisticatedRecovery procedures are difficult.


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Describing and storing data in DBMS

DBMS allows a user to define the data to be stored in termsof data model.Data Model : A data model describes

the structure of a database- data types, relationships, constraints,

a set of basic operations- insert, delete, modify, retrieveMost DBMS today are based on Relational Data Model .


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Introduction to Relational Model

Terminology:

Relation: A Relation is a set of records and attributes. Alsoknown as tuples and columns.

Schema: A description of data in terms of data model is called Schema.

In relational model the schema for a relation specifies its name, the nameof each field (or attribute or column) and the type of each field.

Students ( id : numbers, name : text, age : integer, )Id Name Age

54 Ashish 2155 Akshay 25

56 Anu 21


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We can specify the Integrity Constraints on relations : are conditionsthat the records in a relation must satisfy.

E.g. employee id should only consist of numbers.


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Users may be divided into:-

those who actually use and control the content(called Actors on the Scene ) those who enable the database to be developedand the DBMS software to be designed andimplemented (called Workers Behind the

Scene ) .

Database User


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Actors on the scene

Database administrators:

He is responsible for authorizing access to database,security, system response time.

Database User


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1. Design of the Conceptual and physical schemas: throughinteraction with the end users.

2. Security and Authorization : creating of groups, passwords.

3. Data availability and recovery from failure

4. Database tuning : to maintain the performance by changingconceptual and physical schema.

5. Creating users: It gives some responsibilities to some users which canaccess the database & that database cant access by other user.

6.Deciding information content of database: DBA identifies

information to be recorded about the entities.

Task perform by DBA:


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Actors on the scene

End-users: are the people whose jobs require accessto the database for querying, updating and generatingreports, the database primarily exists for their use.

System administrator : hardware system support

Database User


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Workers on the scene

1. Database Designers:

responsible to define the content, thestructure, the constraints, and functions ortransactions against the database.

They must communicate with the end-usersand understand their needs.

design database structure

Database User


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Workers on the scene

2. System analyst and programmers :implement application programs

3. Database systems programmerWrites the database software itself

4. Application developersWrite software to allow end users to interfacewith the database system

Database User


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End-users End Users: are the people whose jobs require access to the database forquerying, updating and generating reports, the database primarily existsfor their use.

Categories/Types of End-users

1. Casual End Users: occasionally use database, needdifferent information each time. They are typically middleor high level managers.

2. Nave or Parametric end users: main users of database,mostly query and update the database. Use standard typesof queries and updates called canned transactions. E.g.clerks for hotels, airline, etc.


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Categories/Types of End-users

3. Sophisticated end users:these include business analysts, scientists,engineers, others thoroughly familiar with thesystem capabilities and have good knowledge of DBMS.

4. Stand alone users:

Who maintain database for personal use andmaintain personal database by using ready madeprograms. E.g. tax package.


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Webforms Application front

ends

SQL interface

Plan executor

Operator Evaluator Optimizer

parser Shows interaction

Query EvaluationEngine

TransactionManager

Lock manager

Files andAccessBuffer

Manager Disk space

Manager

Recovery

Manager

Index Files

DataFiles

System catalogShows references

Database

Structure of DBMS

SQL commands


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Query Evaluation Engine : It consists of four parts.

a. Parser : A parser breaks data into smaller elements,according to a set of rules that describe its structure.

b. Query Optimizer : uses information about how the data isstored to produce an efficient execution plan for evaluatingthe query.

c. Operator Evaluator : Translates SQL query into executableform and runs it.

d. Plan Executor: Creates an plan to execute the query.


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Files and Access Methods: In DBMS data is storedand organised into files. Each file consists of Pages andPages stores records. In records actual data is stored.

DBMS Creates different types of file like Heap file,index file, unsorted files. So this layer works with file

and there access methods.


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Buffer Manager : It manages the pages which are brought fromdisk to main memory by Files and Access methods.

Disk Space Manager : this layer provides routines to higher layers to allocate, deallocate , read and write pages in disk.

Recovery Manager: responsible for maintaing log, and restoringthe system to a consistent state after a crash.

Transaction Manager: Deals with concurrency control andrecovery.

Lock Manager: keeps track of requests for locks and grants lock on database objects when they become available.


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Figure The Three-schema architecture


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DBMS Architecture1. An Internal Schema (internal level)

describes physical storage structurerelated to the physical data model

2. A Conceptual Schema (conceptual level) describes whole database structure

data types, constraints, user operations,hides the details of storage structure.Also known as Logical Schema.


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DBMS Architecture ( cont )3. External Schemas (external level)

Each external schema describes the part of thedatabase that a particular user group isinterested . E.g. views


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Data IndependenceThree Schema Architecture provide the capacity to change the schemaat one level of a database system without having to change the schemaat the next higher level.

Logical Data Independence : is the capacity to change the conceptualschema without having to change external schema or applicationprograms.

Physical Data Independence: is the capacity to change the internalschema without having to change the conceptual schema .


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Introduction to Data ModelsHierarchical modelNetwork modelRelational modelObject Oriented modelObject relational model

A database model is an organizing principle that specifies particularmechanisms for data storage and retrieval.


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Hierarchical ModelOldest data model. Information Management System (IMS) was thefirst hierarchical database developed by North american rockwell andIBM.The hierarchical model organizes data elements as tabular rows, onefor each instance of an entity.

Deputy GM 1Department 1

Employee 1Employee 2

Deputy GM 2Department 2

Employee 3

Employee 5Employee 4

General Manager


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Advantages of Hierarchical Model

Simplicity : relationship between the various layers is logically

simple.

Data Security : It is the first model that provided security and

enforced by DBMS

Data Integrity : It is based on parent / child relationship, so there

is always a link between child and parent node.

Efficiency: it is efficient when there are many transactions using

data whose relationship is fixed.


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Implementation of Complexity: difficulty to implement bydatabase designers and good knowledge of physical database.

Database Management Problems : change in database requires

change in application programs. Lack of structural independence: structural independenceexists when the changes to the database structure does not affectthe DBMs ability to access data. Hierarchical DBMS usesphysical storage paths to navigate to different data segments.

Programming Complexity : Application programmers mustaware of data segments access paths.

Disadvantages of HierarchicalModel


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Network ModelNetwork model replaces Hierarchical tree with a graph thus allowing more

general connections among the nodes. For e.g. (n:n) relationships or it allows arecord to have more than one parent.

Real time example : suppose an employee works for two departments. Or inbanking an person can have two accounts.


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Advantages of Network Model:

Conceptual Simplicity: Conceptually simple and easy to design.

Capability to handle more relationship types: Network modelcan handle one to many and many-to-many relationships.

Ease of data access : An application can access owner record andthen all member records, if any member record have more thanone owner, then application can move to other owner also.

Data Integrity: Model does not allow a member to exist withoutan owner.

Data Independence: Provide better independence thanHierarchical model. An change in data does not affect application

program.


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Disadvantages of Network Model.

System Complexity: Network model provides navigationalaccess to the data in which the data are accessed one record at atime. Which requires DBA, database designers, application

programmers and even end users to be familiar with data access

paths.

Absence of Structural Independence: Structural change indatabase cause change in application programs becausenavigational access method exists.


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Relational Model requires database designer to represent

real world entities into tables which is difficult.

Whereas Object Oriented model represents an entity as aCLASS. A Class represents both object attributes as well as

the behavior of the entity.

For e.g. a BOOK Class have attributes ISBN, Title, Publisheretc. but also procedure that imitate actions such as

UpdatePrice, Issue, Return.

Object Oriented Model


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Capability to handle large no of different data types: In this model wecan store voices, animations, pictures etc.

Combination of Object-oriented programming and database

technology: Now database technology have benefits of object orientedprogramming.Improves Productivity: New features like inheritance, polymorphism,dynamic binding improves the database applications.

Advantages


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Difficult to maintain: Major updates in databaserequires changes in class specifications.Not suited for all applications: Not suitable for smallorganizations because of high costs.

Disadvantage of Object Oriented Model :


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It combines the advantages of modern object orientedprogramming language with relational database features.E.g. are IBM DB2 Universal Server, Oracle 8 etc.

Object Relational Model

Advantages of Object Relational Model

1. Provides advantages of Relational Model, while resolving known

weakness of the Model.

2. Reuse and Sharing: Extended Server to perform standard functionscentrally.

3. Custom data types: Developers can use custom data types.

4. Logical Independence from Data


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Complexity: because of complex data relationship it is difficult to

model.

Increased CostStill under immature stage: some of the concepts are still developing or

unproven.

Disadvantage of Object Relational Model


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Queries in a DBMSQuerying a DBMS means retrieving the data from the database. Forthis DBMS provides a specialized language called query language.

DBMS provides DDL and DML

DDL Data Manipulation LanguageSDL Storage Definition LanguageVDL View Definition LanguageDML Data Manipulation Language

(For data manipulations like insertion, deletion,update, retrieval, etc.)


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DDL is used by DBA to define the Conceptual Schema.

SDL is used to specify the internal Schema.

The mapping between internal and conceptual schema can be done ineither one of these language.

VDL is used to specify the views and their mappings to the conceptual

schema.

Once the database Schemas are compiled and database is populated with data, users must have some means to manipulatethe database. Like insertion, retrieval, deletion and modificationof data.

For this the Data Manipulation Language (DML) is used.

lec-1 introduction to database systems

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