database systems thomas connolly ch01

8/14/2019 Database systems Thomas Connolly ch01

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Chapter 1

Introduction to Databases

Transparencies

Pearson Education Limited 1995, 2005


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Chapter 1 - Objectives

x Typical functions of a DBMS.

x Major components of the DBMS environment.

x Personnel involved in the DBMS environment.

x History of the development of DBMSs.

x Advantages and disadvantages of DBMSs.



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Examples of Database Applications

x Purchases from the supermarket

x Purchases using your credit card

x Booking a holiday at the travel agents

x Using the local library

x Taking out insurance

x Renting a video

x Using the Internet

x Studying at university



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File-Based Systems

x Collection of application programs that

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

x Each program defines and manages its own

data.



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File-Based Processing



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Limitations of File-Based Approach

x 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.

x Duplication of data

Same data is held by different programs.

Wasted space and potentially different valuesand/or different formats for the same item.



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Limitations of File-Based Approach

x Data dependence

File structure is defined in the program code.

x Incompatible file formats Programs are written in different languages, and so cannot

easily access each others files.

x

Fixed Queries/Proliferation of application programs Programs are written to satisfy particular functions.

Any new requirement needs a new program.



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Database Approach

x Arose because: Definition of data was embedded in application

programs, rather than being stored separately andindependently.

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

x Result: the database and Database Management System

(DBMS).



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Database

x Shared collection of logically related data (anda description of this data), designed to meet theinformation needs of an organization.

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

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



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Database Management System (DBMS)

x A software system that enables users to define,

create, maintain, and control access to the

database.

x (Database) application program: a computer

program that interacts with database by

issuing an appropriate request (SQLstatement) to the DBMS.



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Database Management System (DBMS)



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Database Approach

x Data definition language (DDL).

Permits specification of data types, structures and

any data constraints.

All specifications are stored in the database.

x Data manipulation language (DML).

General enquiry facility (query language) of thedata.



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Database Approach

x Controlled access to database may

include:

a security system

an integrity system

a concurrency control system

a recovery control system

a user-accessible catalog.



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Views

x Allows each user to have his or her own view of

the database.

x A view is essentially some subset of the

database.



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Views - Benefits

x Reduce complexity

x Provide a level of security

x Provide a mechanism to customize the

appearance of the database

x Present a consistent, unchanging picture of the

structure of the database, even if the

underlying database is changed



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Components of DBMS Environment



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x Hardware

Can range from a PC to a network of computers.

x Software

DBMS, operating system, network software (ifnecessary) and also the application programs.

x Data

Used by the organization and a description of

this data called the schema.



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x Procedures

Instructions and rules that should be applied to

the design and use of the database and DBMS.

x People



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Roles in the Database Environment

x Data Administrator (DA)

x Database Administrator (DBA)

x

Database Designers (Logical and Physical)x Application Programmers

x End Users (naive and sophisticated)



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History of Database Systems

x First-generation Hierarchical and Network

x Second generation Relational

x Third generation Object-Relational

Object-Oriented



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Advantages of DBMSs

x Control of data redundancy

x Data consistency

x More information from the same amount of

datax Sharing of data

x Improved data integrity

x Improved security

x Enforcement of standards

x Economy of scale



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Advantages of DBMSs

x Balance conflicting requirements

x Improved data accessibility and responsiveness

x Increased productivity

x Improved maintenance through data

independence

x Increased concurrency

x Improved backup and recovery services



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Disadvantages of DBMSs

x Complexity

x Size

x Cost of DBMS

x Additional hardware costs

x Cost of conversion

x Performance

x Higher impact of a failure


database systems thomas connolly ch01

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