introduction databases

8/3/2019 Introduction Databases

1/30

1

Introduction to Databases

Database Systems Concepts


2/30

2

Objectives

Some common uses of database systems. Characteristics of file-based systems. Database and Database Management System (DBMS). Advantages and disadvantages of DBMSs.

Purpose of three-level database architecture. Contents of external, conceptual, and internal levels. Meaning of logical and physical data independence.

Distinction between DDL and DML.


3/30

3

Examples of Database Applications Purchases from the supermarket Purchases using your credit card Booking a holiday at the travel agents Using the local library Taking out insurance Renting a video Using the Internet Studying at university

Pearson Education Limited 1995, 2005


4/30

4

File-Based Systems Collection of application programs that

perform services for the end users (e.g. reports).

Each program defines and manages its owndata.


5/30

5

File-Based Processing


6/30

6

Limitations of File-Based Approach Separation and isolation of data

Each program maintains its own set of data. Users of one program may be unaware of

potentially useful data held by other programs.

Duplication of data

Same data is held by different programs. Wasted space and potentially different valuesand/or different formats for the same item.


7/30

7

Limitations of File-Based Approach Data dependence

File structure is defined in the program code.

Incompatible file formats Programs are written in different languages, and so

cannot easily access each others files.

Fixed Queries/Proliferation of applicationprograms Programs are written to satisfy particular functions. Any new requirement needs a new program.


8/30

8

Database Approach Arose because:

Definition of data was embedded in applicationprograms, rather than being stored separately andindependently.

No control over access and manipulation of databeyond that imposed by application programs.

Result: the database and Database Management System

(DBMS).


9/30

9

Database Shared collection of logically related data (and

a description of this data), designed to meet theinformation needs of an organization.

System catalog (metadata) provides descriptionof data to enable program data independence.

Logically related data comprises entities,attributes, and relationships of anorganizations information.


10/30

10

Database Management System

(DBMS) A software system that enables users to define,create, maintain, and control access to thedatabase.

(Database) application program: a computerprogram that interacts with database by

issuing an appropriate request (SQLstatement) to the DBMS.


11/30

11

Database Management System

(DBMS)


12/30

12

Database Approach Controlled access to database may

include: a security system an integrity system a concurrency control system a recovery control system

a user-accessible catalog.


13/30

13

Components of DBMS Environment


14/30

14

Components of DBMS Environment Hardware

Can range from a PC to a network Software

DBMS, operating system, application programs. Data

and a description of this data (schema) Procedures

Instructions and rules that should be applied to the designand use of the database and DBMS.

People


15/30

15

Roles in the Database Environment

Data Administrator (DA ) Database Administrator (DBA)

Database Designers (Logical and Physical) Application Programmers End Users (naive and sophisticated)


16/30

16

Advantages of DBMSs Control of data redundancy Data consistency More information from the same amount of

data Sharing of data Improved data integrity Improved security Enforcement of standards Economy of scale


17/30

17

Advantages of DBMSs Balance conflicting requirements Improved data accessibility and responsiveness Increased productivity Improved maintenance through data

independence Increased concurrency Improved backup and recovery services


18/30

18

Disadvantages of DBMSs Complexity Size Cost of DBMS Additional hardware costs Cost of conversion Performance Higher impact of a failure


19/30

19

Database EnvironmentThree Level Architecture


20/30

20

Objectives of Three-Level

Architecture All users should be able to access same data.

A users view is immune to changes made inother views.

Users should not need to know physicaldatabase storage details.


21/30

21

Objectives of Three-LevelArchitecture

DBA should be able to change database storagestructures without affecting the users views.

Internal structure of database should beunaffected by changes to physical aspects of storage.

DBA should be able to change conceptualstructure of database without affecting all users.


22/30

22

ANSI-SPARC Three-Level Architecture


23/30

23

ANSI-SPARC Three-Level

Architecture External Level Users view of the database. Describes that part of database that is relevant to a

particular user.

Conceptual Level Community view of the database. Describes what data is stored in database and

relationships among the data.


24/30

24

ANSI-SPARC Three-Level

Architecture Internal Level

Physical representation of the database on thecomputer.

Describes how the data is stored in the database.


25/30

25

Differences between Three Levels of ANSI-SPARC Architecture


26/30

26

Data Independence Logical Data Independence

Refers to immunity of external schemas to changesin conceptual schema.

Conceptual schema changes (e.g. addition/removalof entities).

Should not require changes to external schema orrewrites of application programs.


27/30

27

Data Independence Physical Data Independence

Refers to immunity of conceptual schema to changesin the internal schema.

Internal schema changes (e.g. using different fileorganizations, storage structures/devices).

Should not require change to conceptual or externalschemas.


28/30

28

Data Independence and the ANSI-SPARC Three-Level Architecture


29/30

29

Database Languages Data Definition Language (DDL)

Allows the DBA or user to describe and nameentities, attributes, and relationships required for

the application plus any associated integrity and security

constraints.


30/30

30

Database Languages Data Manipulation Language (DML)

Provides basic data manipulation operations ondata held in the database.

Procedural DML allows user to tell system exactly how to manipulate

data. Non-Procedural DML

allows user to state what data is needed rather thanhow it is to be retrieved.

Fourth Generation Languages (4GLs)

introduction databases

Documents