Chapter 1 Introduction to Databases © Pearson Education Limited 1995, 2005

File-Based Systems u Collection of application programs that perform services for the end users (e.g. reports). u Each program defines and manages its own data. © Pearson Education Limited 1995, 2005

File-Based Processing © Pearson Education Limited 1995, 2005

Limitations of File-Based Approach u Duplication of data –Same data is held by different programs. u 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. –Wasted space and potentially different values and/or different formats for the same item. © Pearson Education Limited 1995, 2005

Limitations of File-Based Approach u Data dependence –File structure is defined in the program code. u Incompatible file formats –Programs are written in different languages, and so cannot easily access each other’s files. u Fixed Queries/Proliferation of application programs –Programs are written to satisfy particular functions. –Any new requirement needs a new program. © Pearson Education Limited 1995, 2005

Database Approach u Database approch arose because, file-based approach had following problems: –Definition of data was embedded in application programs, rather than being stored separately and independently. –No control over access and manipulation of data beyond that imposed by application programs. u Result: –the database and Database Management System (DBMS). © Pearson Education Limited 1995, 2005

Database u Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization. u System catalog (metadata) provides description of data to enable program–data independence. u Logically related data comprises entities, attributes, and relationships of an organization’s information. © Pearson Education Limited 1995, 2005

Database Management System (DBMS) u A software system that enables users to define, create, maintain, and control access to the database. u (Database) application program: a computer program that interacts with database by issuing an appropriate request (SQL statement) to the DBMS. © Pearson Education Limited 1995, 2005

Database Management System (DBMS) © Pearson Education Limited 1995, 2005

Database Approach u Data definition language (DDL). –Permits specification of data types, structures and any data constraints. –All specifications are stored in the database. u Data manipulation language (DML). –General enquiry facility (query language) of the data. © Pearson Education Limited 1995, 2005

DDL Example CREATE TABLE "PRIVATEOWNER" ( "OWNERNO" NUMBER, "FNAME" VARCHAR2(40), "LNAME" VARCHAR2(40), "ADDRESS" VARCHAR2(50), "TELNO" VARCHAR2(12), CONSTRAINT "PRIVATEOWNER_PK" PRIMARY KEY ("OWNERNO") ENABLE ) /

DML example SELECT * FROM "PRIVATEOWNER" WHERE OWNERNO>3;

Database Approach u Controlled access to database may include: –a security system –an integrity system –a concurrency control system –a recovery control system –a user-accessible catalog. © Pearson Education Limited 1995, 2005

Views u Allows each user to have his or her own view of the database. u A view is essentially some subset of the database. © Pearson Education Limited 1995, 2005

Views - Benefits u Reduce complexity u Provide a level of security u Provide a mechanism to customize the appearance of the database u Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed © Pearson Education Limited 1995, 2005

Roles in the Database Environment u Data Administrator (DA) u Database Administrator (DBA) u Database Designers (Logical and Physical) u Application Programmers u End Users (naive and sophisticated) © Pearson Education Limited 1995, 2005

History of Database Systems u First-generation –Hierarchical and Network u Second generation –Relational u Third generation –Object-Relational –Object-Oriented © Pearson Education Limited 1995, 2005

Advantages of DBMSs u Control of data redundancy u Data consistency u More information from the same amount of data u Sharing of data u Improved data integrity u Improved security u Enforcement of standards u Economy of scale © Pearson Education Limited 1995, 2005

Disadvantages of DBMSs u Complexity u Size u Cost of DBMS u Additional hardware costs u Cost of conversion u Performance u Higher impact of a failure © Pearson Education Limited 1995, 2005