1. 1 Chapter 2 Database Environment Transparencies © Pearson Education Limited 1995, 2005

2. 2 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 Distinction between DDL and DML. u A classification of data models. © Pearson Education Limited 1995, 2005

3. 3 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. © Pearson Education Limited 1995, 2005

4. 4 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. © Pearson Education Limited 1995, 2005

5. 5 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. © Pearson Education Limited 1995, 2005

6. 6 ANSI-SPARC Three-Level Architecture © Pearson Education Limited 1995, 2005

7. 7 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. © Pearson Education Limited 1995, 2005

8. 8 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. © Pearson Education Limited 1995, 2005

9. 9 Differences between Three Levels of ANSI- SPARC Architecture © Pearson Education Limited 1995, 2005

10. 10 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. © Pearson Education Limited 1995, 2005

11. 11 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. u Fourth Generation Languages (4GLs) © Pearson Education Limited 1995, 2005

12. 12 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. © Pearson Education Limited 1995, 2005

13. 13 Data Model u Purpose –To represent data in an understandable way. u Categories of data models include: –Object-based –Record-based –Physical. © Pearson Education Limited 1995, 2005

14. 14 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 © Pearson Education Limited 1995, 2005

15. 15 Relational Data Model © Pearson Education Limited 1995, 2005

16. 16 Network Data Model © Pearson Education Limited 1995, 2005

17. 17 Hierarchical Data Model © Pearson Education Limited 1995, 2005

18. 18 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. © Pearson Education Limited 1995, 2005

19. 19 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. u Authorization Services. u Support for Data Communication. u Integrity Services. u Services to Promote Data Independence. u Utility Services. © Pearson Education Limited 1995, 2005

20. 20 Components of a DBMS © Pearson Education Limited 1995, 2005

21. 21 Multi-User DBMS Architectures u Teleprocessing u File-server u Client-server © Pearson Education Limited 1995, 2005

22. 22 Teleprocessing u Traditional architecture. u Single mainframe with a number of terminals attached. u Trend is now towards downsizing. © Pearson Education Limited 1995, 2005

23. 23 File-Server u File-server is connected to several workstations across a network. u Database resides on file-server. u DBMS and applications run on each workstation. u Disadvantages include: –Significant network traffic. –Copy of DBMS on each workstation. –Concurrency, recovery and integrity control more complex. © Pearson Education Limited 1995, 2005

24. 24 File-Server Architecture © Pearson Education Limited 1995, 2005

25. 25 Traditional Two-Tier Client-Server u Client (tier 1) manages user interface and runs applications. u Server (tier 2) holds database and DBMS. u Advantages include: –wider access to existing databases; –increased performance; –possible reduction in hardware costs; –reduction in communication costs; –increased consistency. © Pearson Education Limited 1995, 2005

26. 26 Traditional Two-Tier Client-Server © Pearson Education Limited 1995, 2005

27. 27 Traditional Two-Tier Client-Server © Pearson Education Limited 1995, 2005

28. 28 Three-Tier Client-Server u Client side presented two problems preventing true scalability: –‘Fat’ client, requiring considerable resources on client’s computer to run effectively. –Significant client side administration overhead. u By 1995, three layers proposed, each potentially running on a different platform. © Pearson Education Limited 1995, 2005

29. 29 Three-Tier Client-Server u Advantages: –‘Thin’ client, requiring less expensive hardware. –Application maintenance centralized. –Easier to modify or replace one tier without affecting others. –Separating business logic from database functions makes it easier to implement load balancing. –Maps quite naturally to Web environment. © Pearson Education Limited 1995, 2005

30. 30 Three-Tier Client-Server © Pearson Education Limited 1995, 2005