1. 1 Chapter 1 Introduction to Databases Transparencies

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

16. 16 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.

17. 17 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

18. 18 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)

19. 19 History of Database Systems u First-generation –Hierarchical and Network u Second generation –Relational u Third generation –Object Relational –Object-Oriented

20. 20 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

21. 21 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

22. 22 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

23. 23 Chapter 2 - Objectives u Purpose of three-level database architecture. u Contents of external, conceptual, and internal levels. u Purpose of external/conceptual and conceptual/internal mappings. u Meaning of logical and physical data independence. u Distinction between DDL and DML. u A classification of data models.

24. 24 Chapter 2 - Objectives u Purpose/importance of conceptual modeling. u Typical functions and services a DBMS should provide. u Software components of a DBMS. u Meaning of client–server architecture and advantages of this type of architecture for a DBMS. u Function and uses of Transaction Processing Monitors. u Function and importance of the system catalog.

25. 25 Objectives of Three-Level Architecture u All users should be able to access same data. u A user’s view is immune to changes made in other views. u Users should not need to know physical database storage details.

26. 26 Objectives of Three-Level Architecture u DBA should be able to change database storage structures without affecting the users’ views. u Internal structure of database should be unaffected by changes to physical aspects of storage. u DBA should be able to change conceptual structure of database without affecting all users.

27. 27 ANSI-SPARC Three-Level Architecture

28. 28 ANSI-SPARC Three-Level Architecture u External Level –Users’ view of the database. –Describes that part of database that is relevant to a particular user. u Conceptual Level –Community view of the database. –Describes what data is stored in database and relationships among the data.

29. 29 ANSI-SPARC Three-Level Architecture u Internal Level –Physical representation of the database on the computer. –Describes how the data is stored in the database.

30. 30 Differences between Three Levels of ANSI- SPARC Architecture

31. 31 Data Independence u Logical Data Independence –Refers to immunity of external schemas to changes in conceptual schema. –Conceptual schema changes (e.g. addition/removal of entities). –Should not require changes to external schema or rewrites of application programs.

32. 32 Data Independence u Physical Data Independence –Refers to immunity of conceptual schema to changes in the internal schema. –Internal schema changes (e.g. using different file organizations, storage structures/devices). –Should not require change to conceptual or external schemas.

33. 33 Data Independence and the ANSI-SPARC Three-Level Architecture

34. 34 Database Languages u Data Definition Language (DDL) –Allows the DBA or user to describe and name entities, attributes, and relationships required for the application –plus any associated integrity and security constraints.

35. 35 Database Languages u Data Manipulation Language (DML) –Provides basic data manipulation operations on data held in the database. u Procedural DML –allows user to tell system exactly how to manipulate data. u Non-Procedural DML –allows user to state what data is needed rather than how it is to be retrieved.

36. 36 Database Languages u Fourth Generation Language (4GL) –Query Languages –Forms Generators –Report Generators –Graphics Generators –Application Generators.

37. 37 Data Model Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization. u Data Model comprises: –a structural part; –a manipulative part; –possibly a set of integrity rules.

38. 38 Data Model u Purpose –To represent data in an understandable way. u Categories of data models include: –Object-based –Record-based –Physical.

39. 39 Data Models u Object-Based Data Models –Entity-Relationship –Semantic –Functional –Object-Oriented. u Record-Based Data Models –Relational Data Model –Network Data Model –Hierarchical Data Model. u Physical Data Models

40. 40 Conceptual Modeling u Conceptual schema is the core of a system supporting all user views. u Should be complete and accurate representation of an organization’s data requirements. u Conceptual modeling is process of developing a model of information use that is independent of implementation details. u Result is a conceptual data model.

41. 41 Functions of a DBMS u Data Storage, Retrieval, and Update. u A User-Accessible Catalog. u Transaction Support. u Concurrency Control Services. u Recovery Services.

42. 42 Functions of a DBMS u Authorization Services. u Support for Data Communication. u Integrity Services. u Services to Promote Data Independence. u Utility Services.

43. 43 Components of a DBMS

44. 44 Components of Database Manager (DM)

45. 45 Client-Server u Server holds the database and the DBMS. u Client manages user interface and runs applications. u Advantages include: –wider access to existing databases; –increased performance; –possible reduction in hardware costs; –reduction in communication costs; –increased consistency.

46. 46 Client-Server Architecture

47. 47 System Catalog u Repository of information (metadata) describing the data in the database. u Typically stores: –names of authorized users; –names of data items in the database; –constraints on each data item; –data items accessible by a user and the type of access. u Used by modules such as Authorization Control and Integrity Checker.

48. 48 Information Resource Dictionary System (IRDS) u Response to an attempt to standardize data dictionary interfaces. u Objectives: –extensibility of data; –integrity of data; –controlled access to data.