ch02 - Database Environment.ppt chapter 2
- 1. Chapter 2 Database Environment Pearson Education © 2014
- 2. Chapter 2 - Objectives Purpose of three-level database architecture. Contents of external, conceptual, and internal levels. Purpose of external/conceptual and conceptual/internal mappings. Meaning of logical and physical data independence. Distinction between DDL and DML. A classification of data models. Pearson Education © 2014 2
- 3. Chapter 2 - Objectives Purpose/importance of conceptual modeling. Typical functions and services a DBMS should provide. Function and importance of system catalog. Software components of a DBMS. Meaning of client–server architecture and advantages of this type of architecture for a DBMS. Function and uses of Transaction Processing Monitors. 3 Pearson Education © 2014
- 4. Objectives of Three-Level Architecture All users should be able to access same data. A user’s view is immuned to changes made in other views. Users should not need to know physical database storage details. Pearson Education © 2014 4
- 5. Objectives of Three-Level Architecture DBA should be able to change database storage structures without affecting the users’ views. Internal structure of database should be unaffected by changes to physical aspects of storage. DBA should be able to change conceptual structure of database without affecting all users. Pearson Education © 2014 5
- 7. ANSI-SPARC Three-Level Architecture External Level Users’ view of the database. Describes that part of database that is relevant to a particular user. Conceptual Level Community view of the database. Describes what data is stored in database and relationships among the data. Pearson Education © 2014 7
- 8. ANSI-SPARC Three-Level Architecture Internal Level Physical representation of the database on the computer. Describes how the data is stored in the database. Pearson Education © 2014 8
- 9. Differences between Three Levels of ANSI- SPARC Architecture Pearson Education © 2014 9
- 10. Data Independence Changes in the levels should not affect other levels in the Three-Level Architecture; 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. Pearson Education © 2014 10
- 11. Data Independence 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. Pearson Education © 2014 11
- 12. Data Independence and the ANSI-SPARC Three-Level Architecture Pearson Education © 2014 12
- 13. Database Languages 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 © 2014 13
- 14. Database Languages Data Manipulation Language (DML) Provides basic data manipulation operations on data held in the database. Procedural DML allows user to tell system exactly how to manipulate data. Non-Procedural DML allows user to state what data is needed rather than how it is to be retrieved. Fourth Generation Languages (4GLs) Other programming languages embedded with DML Pearson Education © 2014 14
- 15. Data Model Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization. Data Model comprises: a structural part; a manipulative part; possibly a set of integrity rules. Pearson Education © 2014 15
- 16. Data Model Purpose To represent data in an understandable way. Categories of data models include: Object-based Record-based Physical. Pearson Education © 2014 16
- 17. Data Models Object-Based Data Models Entity-Relationship Semantic Functional Object-Oriented. Record-Based Data Models Relational Data Model Network Data Model Hierarchical Data Model. Physical Data Models Pearson Education © 2014 17
- 18. Relational Data Model Pearson Education © 2014 18
- 19. Network Data Model Pearson Education © 2014 19
- 20. Hierarchical Data Model Pearson Education © 2014 20
- 21. Conceptual Modeling Conceptual schema is the core of a system supporting all user views. Should be complete and accurate representation of an organization’s data requirements. Conceptual modeling is process of developing a model of information use that is independent of implementation details. Result is a conceptual data model (E-R diagram). Pearson Education © 2014 21
- 22. Functions of a DBMS Data Storage, Retrieval, and Update. A User-Accessible Catalog. Transaction Support. Concurrency Control Services. Recovery Services. Pearson Education © 2014 22
- 23. Functions of a DBMS Authorization Services. Support for Data Communication. Integrity Services. Services to Promote Data Independence. Utility Services. Pearson Education © 2014 23
- 24. System Catalog Repository of information (metadata) describing the data in the database. One of the fundamental components of DBMS. Typically stores: names, types, and sizes of data items; constraints on the data; names of authorized users; data items accessible by a user and the type of access; usage statistics. Pearson Education © 2014 24
- 25. Components of a DBMS Pearson Education © 2014 25
- 26. Components of Database Manager Pearson Education © 2014 26
- 27. Multi-User DBMS Architectures Teleprocessing File-server Client-server Pearson Education © 2014 27
- 28. Teleprocessing Traditional architecture. Single mainframe with a number of terminals attached. Trend is now towards downsizing. Pearson Education © 2014 28
- 29. File-Server File-server is connected to several workstations across a network. Database resides on file-server. DBMS and applications run on each workstation. Disadvantages include: Significant network traffic. Copy of DBMS on each workstation. Concurrency, recovery and integrity control more complex. Pearson Education © 2014 29
- 30. File-Server Architecture Pearson Education © 2014 30
- 31. Traditional Two-Tier Client-Server Client (tier 1) manages user interface and runs applications. Server (tier 2) holds database and DBMS. Advantages include: wider access to existing databases; increased performance; possible reduction in hardware costs; reduction in communication costs; increased consistency. Pearson Education © 2014 31
- 32. Traditional Two-Tier Client- Server Pearson Education © 2014 32
- 33. Traditional Two-Tier Client- Server Pearson Education © 2014 33
- 34. Three-Tier Client-Server 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. By 1995, three layers proposed, each potentially running on a different platform. Pearson Education © 2014 34
- 35. Three-Tier Client-Server 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 © 2014 35
- 36. Three-Tier Client-Server Pearson Education © 2014 36
- 37. Transaction Processing Monitors Program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for Online Transaction Processing (OLTP). 37 Pearson Education © 2014
- 38. TPM as middle tier of 3-tier client-server Pearson Education © 2014 38