lec01 introduction to databases

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Chapter 1

Introduction to Databases

Transparencies

Pearson Education Limited 1995, 2005


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Chapter 1 - Objectives

x Some common uses of database systems.x Characteristics of file-based systems.x Problems with file-based approach.x Meaning of the term database.x Meaning of the term Database Management

System (DBMS).



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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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File-Based Processing



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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 applicationprograms 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 thedatabase.

x (Database) application program: a computerprogram 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 mayinclude: 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 thedatabase.



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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 (if

necessary) and also the application programs.x Data

Used by the organization and a descriptionof 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 Programmersx 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 redundancyx Data consistencyx More information from the same amount of

datax Sharing of datax Improved data integrityx Improved securityx Enforcement of standardsx Economy of scale



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Advantages of DBMSs

x Balance conflicting requirementsx Improved data accessibility and responsivenessx Increased productivityx Improved maintenance through data

independencex Increased concurrencyx Improved backup and recovery services



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Disadvantages of DBMSs

x Complexityx Sizex Cost of DBMSx Additional hardware costsx Cost of conversionx Performancex Higher impact of a failure


lec01 introduction to databases

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