1. 1 Introduction to Databases

2. 2 Examples of Database Applications u Purchases from the supermarket u Purchases using your credit card u Booking a holiday at the travel agents u Using the local library u Taking out insurance u Using the Internet u Studying at university

3. 3 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.

4. 4 File-Based Processing

5. 5 Limitations of File-Based Approach 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. u Duplication of data –Same data is held by different programs. –Wasted space and potentially different values and/or different formats for the same item.

6. 6 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.

7. 7 Database Approach u Arose because: –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).

8. 8 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.

9. 9 Database Management System (DBMS) u A software system that enables users to define, create, and maintain the database and that provides controlled access to this database.

10. 10 Database Management System (DBMS)

11. 11 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.

12. 12 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. u A view mechanism. –Provides users with only the data they want or need to use.

13. 13 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.

14. 14 Views u Benefits include: –Reduce complexity; –Provide a level of security; –Provide a mechanism to customize the appearance of the database; –Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed.

15. 15 Components of DBMS Environment u Hardware –Can range from a PC to a network of computers. u Software –DBMS, operating system, network software (if necessary) and also the application programs. u Data –Used by the organization and a description of this data called the schema.

16. 16 Components of DBMS Environment u Procedures –Instructions and rules that should be applied to the design and use of the database and DBMS. u People

17. 17 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

18. 18 Advantages of DBMSs u Balanced conflicting requirements u Improved data accessibility and responsiveness u Increased productivity u Improved maintenance through data independence u Increased concurrency u Improved backup and recovery services

19. 19 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