1. DatabaseIM ISU1 Fundamentals of Database Systems Chapter 2 Database System Concepts and Architecture

2. DatabaseIM ISU2 Data Models  Definition  A set of concepts to describe the structure of a database, and certain constraints that the database should obey  Most data models also include a set of basic operations for specifying retrievals and updates on the database

3. DatabaseIM ISU3 Data Models (cont.)  Categories of data models  Conceptual (high-level, semantic) data models »Provide concepts that are close to the way many users perceive data »e.g., Entity-relationship model, object data model  Physical (low-level, internal) data models »Provide concepts that describe details of how data is stored in the computer

4. DatabaseIM ISU4 Data Models (cont.)  Implementation (record-oriented) data models »Provide concepts that fall between the above two, balancing user views with some computer storage details »e.g., relational model, hierarchical model, network model

5. DatabaseIM ISU5 Data Models (cont.)  History of data models  Relational Model »Proposed in 1970 by E.F. Codd (IBM) »First commercial system in 1981-82 »e.g., ORACLE, SYBASE, SQL Server

6. DatabaseIM ISU6 Data Models (cont.)

7. DatabaseIM ISU7 Data Models (cont.)  Network Model »The first one to be implemented by Honeywell in 1964-65 (IDS System) »Adopted heavily due to the support by CODASYL (CODASYL - DBTG report of 1971) »Later implemented in a large variety of systems - IDMS (Cullinet - now CA), DMS 1100 (Unisys), IMAGE (H.P.), VAX -DBMS (Digital)

8. DatabaseIM ISU8 Data Models (cont.)

9. DatabaseIM ISU9 Data Models (cont.)  Hierarchical Data Model »Implemented in a joint effort by IBM and North American Rockwell around 1965 »Resulted in the IMS family of systems »The most popular model

10. DatabaseIM ISU10 Data Models (cont.)

11. DatabaseIM ISU11 Data Models (cont.)  Object-oriented Data Models »Several models have been proposed for implementing in a database system »One set comprises models of persistent O-O Programming Languages such as C++ (e.g., in OBJECTSTORE or VERSANT), and Smalltalk (e.g., in GEMSTONE) »Additionally, systems like O 2, ORION (at MCC - then ITASCA), IRIS (at H.P.- used in Open OODB) »Object Database Standard: ODMG-93, ODMG-version 2.0, ODMG-version 3.0

12. DatabaseIM ISU12 Data Models (cont.)  Object-Relational Models »Most recent trend, started with Informix Universal Server »Relational systems incorporate concepts from object databases leading to object-relational »Exemplified in the latest versions of Oracle-10i, DB2, and SQL Server and other DBMSs »Standards included in SQL-99 and expected to be enhanced in future SQL standards

13. DatabaseIM ISU13 Schemas vs Instances  Database Schema  The description of a database  Includes descriptions of the database structure and the constraints that should hold on the database  Can be displayed as a diagram (called schema diagram)  Database schema changes very infrequently

14. DatabaseIM ISU14 Schemas vs Instances (cont.)  Example schema diagram

15. DatabaseIM ISU15 Schemas vs Instances (cont.)  Database Instance  The actual data stored in a database at a particular moment in time  Also called database state (or occurrence)  The database state changes every time the database is updated »e.g., insert or delete a record

16. DatabaseIM ISU16 Schemas vs Instances (cont.)  Example database state

17. DatabaseIM ISU17 Schema Architecture  Three-Schema Architecture  Internal schema »Describe data storage structures and access paths at the internal level »Typically uses a physical data model  Conceptual schema »Describe the structure and constraints for the database at the conceptual level »Uses a conceptual or an implementation data model

18. DatabaseIM ISU18 Schema Architecture (cont.)  External schemas »Describe the various user views at the external level to »Usually uses the same data model as the conceptual level  Purposes »Support program-data independence »Support of multiple views of the data

19. DatabaseIM ISU19 DBMS Architecture (cont.)

20. DatabaseIM ISU20 Data Independence  Logical Data Independence  The capacity to change the conceptual schema without having to change the external schemas and their application programs  Only view definition and the mapping need be change  e.g., Changing the Grade_Report

21. DatabaseIM ISU21 DBMS Architecture (cont.)

22. DatabaseIM ISU22 Data Independence (cont.)  Physical Data Independence  The capacity to change the internal schema without having to change the conceptual schema  e.g., providing an access path by Semester and Year should not change query “list all sections offered in fall 1998”

23. DatabaseIM ISU23 DBMS Languages  Data Definition Language (DDL)  Used by the DBA and database designers to specify the conceptual schema  In many DBMSs, DDL is also used to define conceptual and external schemas (views)  In some DBMSs, »Internal: storage definition language (SDL) »External: view definition language (VDL)

24. DatabaseIM ISU24 DBMS Languages (cont.)

25. DatabaseIM ISU25 DBMS Languages (cont.)  Data Manipulation Language (DML)  Used to specify database retrievals and updates  DML commands (data sublanguage) can be embedded in a general-purpose programming language, such as COBOL, PL/1, C/C++  Alternatively, stand-alone DML commands can be applied directly (query language)

26. DatabaseIM ISU26 DBMS Languages (cont.)  Example in SQL SELECT BDATE, ADDRESS FROM EMPLOYEE WHEREFNAME='John' AND MINIT='B' AND LNAME='Smith'

27. DatabaseIM ISU27 DBMS Languages (cont.)  Example of embedded SQL EXEC SQL declare c cursor for select customer-name, customer-city from depositor, customer, account where depositor.customer-name = customer.customer-name and depositor account-number = account.account-number and account.balance > :amount END-EXEC

28. DatabaseIM ISU28 Database System Environment  DBMS component modules  Database system utilities  Tools  CASE tools, data dictionary  Application environment  e.g., PowerBuilder  Communication facilities

29. DatabaseIM ISU29 DBMS Component Modules

30. DatabaseIM ISU30 DBMS Architectures  Centralized DBMS  Combines everything into single system including- DBMS software, hardware, application programs, and user interface processing software  User can still connect through a remote terminal – however, all processing is done at centralized site

31. DatabaseIM ISU31 DBMS Architectures (cont.)  A physical centralized architecture

32. DatabaseIM ISU32 DBMS Architectures (cont.)  Basic Client-Server Architectures  Specialized Servers with Specialized functions »Print server »File server »DBMS server »Web server »Email server  Clients can access the specialized servers as needed

33. DatabaseIM ISU33 DBMS Architectures (cont.)  Logical client-server architecture

34. DatabaseIM ISU34 DBMS Architectures (cont.)  Two Tier Client-Server Architecture  A client program may connect to several DBMSs, sometimes called the data sources  In general, data sources can be files or other non-DBMS software that manages data  Other variations of clients are possible »in some object DBMSs, more functionality is transferred to clients including data dictionary functions, optimization and recovery across multiple servers, etc.

35. DatabaseIM ISU35 DBMS Architectures (cont.)  Three Tier Client-Server Architecture  Common for Web applications  Intermediate Layer called Application Server or Web Server: »Stores the web connectivity software and the business logic part of the application used to access data from database server »Acts like a conduit for sending partially processed data between the database server and the client.  Three-tier Architecture Can Enhance Security »Database server only accessible via middle tier »Clients cannot directly access database server

36. DatabaseIM ISU36 DBMS Architectures (cont.)  Logical three tier client-server architecture

37. DatabaseIM ISU37 Classification of DBMSs  Based on the data model used  Traditional: Relational, Network, Hierarchical  Emerging: Object-oriented, Object-relational  Based on the number of users  Single-user (typically used with micro- computers)  multi-user (most DBMSs)

38. DatabaseIM ISU38 Classification of DBMSs (cont.)  Based on the number of sites  Centralized (uses a single computer with one database)  Distributed (uses multiple computers, multiple databases) »Homogeneous »Heterogeneous (Federated DBMS)