Database Systems

1. Database Systems Week 1 Introduction By Zekrullah Popal

2. Data vs. Information • Data: • Raw facts; building blocks of information • Unprocessed information • Information: • Data processed to reveal meaning • Accurate, relevant, and timely information is key to good decision making • Good decision making is key to survival in global environment

3. Database definitions: • Def 1: A shared collection of logically related data, designed to meet the information needs of multiple users in an organization. The term database is often erroneously referred to as a synonym for a “database management system (DBMS)”. They are not equivalent and it will be explained in the next section.

4. Database definitions (cont…) • Def 2: A collection of data: part numbers, product codes, customer information, etc. It usually refers to data organized and stored on a computer that can be searched and retrieved by a computer program. • Def 3: A data structure that stores metadata, i.e. data about data. More generally we can say an organized collection of information.

5. Database definitions (cont…) • Def 4: A collection of information organized and presented to serve a specific purpose. (A telephone book is a common database.) A computerized database is an updated, organized file of machine readable information that is rapidly searched and retrieved by computer.

6. Database definitions (cont…) • Def 5: An organized collection of information in computerized format. • Def 6: A collection of related information about a subject organized in a useful manner that provides a base or foundation for procedures such as retrieving information, drawing conclusions, and making decisions. • Def 7: A Computerized representation of any organizations flow of information and storage of data.

7. Types of Databases • Single-user: • Supports only one user at a time • Desktop/Personal Databases • Single-user database running on a personal computer • Multi-user: • Supports multiple users at the same time

8. Types of Databases (continued) • Workgroup • Multi-user database that supports a small group of users or a single department • Enterprise • Multi-user database that supports a large group of users or an entire organization

9. Location of Databases • Centralized: • Supports data located at a single site • Distributed: • Supports data distributed across several sites

10. Disadvantages of File Processing • Program-Data Dependence • All programs maintain metadata for each file they use • Duplication of Data • Different systems/programs have separate copies of the same data • Limited Data Sharing • No centralized control of data • Lengthy Development Times • Programmers must design their own file formats • Excessive Program Maintenance • 80% of information systems budget

11. Problems with Data Dependency • Each application programmer must maintain their own data • Each application program needs to include code for the metadata of each file • Each application program must have its own processing routines for reading, inserting, updating and deleting data • Lack of coordination and central control • Non-standard file formats

12. Duplicate Data Figure 1-2 Three file processing systems at Pine Valley Furniture

13. Problems with Data Redundancy • Waste of space to have duplicate data • Causes more maintenance headaches • The biggest problem: • When data changes in one file, could cause inconsistencies • Compromises data integrity

14. SOLUTION: The DATABASE Approach • Central repository of shared data • Data is managed by a controlling agent • Stored in a standardized, convenient form Requires a Database Management System (DBMS)

15. Database Management System • A software system that is used to create, maintain, and provide controlled access to user databases DBMS manages data resources like an operating system manages hardware resources

16. Client/server system architecture

17. Elements of the Database Approach • Enterprise Data Model • Graphical model showing high-level entities and relationships for the organization and the relationship among those entities. • Entity: an object or concept that is important to the business.

19. One customer may place many orders, but each order is placed by a single customer  One-to-many relationship

20. One order has many order lines; each order line is associated with a single order  One-to-many relationship

21. One product can be in many order lines, each order line refers to a single product  One-to-many relationship

22. Therefore, one order involves many products and one product is involved in many orders  Many-to-many relationship

23. Elements of the Database Approach (cont…) • Relational DatabasesDatabase technology involving tables (relations) representing entities and primary/foreign keys representing relationships

24. Relationships established in special columns that provide links between tables

25. Elements of the Database Approach (cont…) • Use of Internet Technology • Networks and telecommunications, distributed databases, client-server • Database Applications • Application programs used to perform database activities (create, read, update, and delete) for database users

26. Application program functions: inserting new data, updating existing data, deleting existing data, reading data for display

27. Advantages of Databases • Program-Data independence • The separation of data description (metadata) from application programs that use the data. • Changing organization’s data with out changing application programs that process that data. • Minimal data redundancy • Previously separate data files are integrated into a single, logical structure. • Some limited redundancy may be desirable to improve database performance.

28. Advantages of Databases (cont…) • Improved data consistency • By eliminating data redundancy we greatly reduce inconsistencies. e.g. customer address stored once • Storage space is not wasted • Increased productivity of application development • Cost and time of new database application is reduced • Using functions, using reports and forms

29. Advantages of Databases (cont…) • Improved data quality • Database designer can specify constraints • Improved data accessibility • Select * from product where product_name= “computer”; • Reduced program maintenance • Changes are easily accommodated e.g. adding new data items, changing data formats

30. Costs and risks of database approach • New, specialized personals • Hire individuals to design and implement, and administer databases • Upgradation of personal if new technology comes to market • Installation and management cost • Install, new release and upgrades, costly software for security • Conversion cost • Legacy system: older application in an organization based on file processing system • Legacy to modern

31. Costs and risks of database approach • Explicit Backup and recovery • Organizational conflicts

33. Figure 1-9 Workgroup database with local area network

34. Figure 1-10 An enterprise data warehouse

36. Components of the Database Environment • CASE Tools – computer-aided software engineering • Repository – centralized storehouse of metadata • Database Management System (DBMS) – software for managing the database • Database – storehouse of the data • Application Programs – software using the data • User Interface – text and graphical displays to users • Data Administrators – personnel responsible for maintaining the database • System Developers – personnel responsible for designing databases and software • End Users – people who use the applications and databases

37. Figure 1-11 Components of the database environment

38. Evolution of DB Systems • Flat files - 1960s - 1980s • Hierarchical – 1970s - 1990s • Network – 1970s - 1990s • Relational – 1980s - present • Object-oriented – 1990s - present • Object-relational – 1990s - present • Data warehousing – 1980s - present • Web-enabled – 1990s - present