DATABASE SYSTEMS

1. DATABASE SYSTEMS Overview

2. DATABASE SYSTEMS • A database may be defined as a collection of interrelated data stored together without harmful or unnecessary redundancy to serve multiple applications • the data are stored so that they are independent of programs which use the data • a common and controlled approach is used in adding new data and in modifying and retrieving existing data within the data base. • The data is structured so as to provide a foundation for future application development.

3. DATABASE SYSTEMS • Components App. 1 Students App. 2 Database system Classes App. 3 Payroll Teachers App. 4 Database

4. DATABASE SYSTEMS • Important considerations • Sharing • Data Integraty • Redundancy • Growth • Logical data independence • Physical data independence

5. DATABASE SYSTEMS • Redundancy • A database should minimize redundancy. • controlled or minimal redundancy • for capability to recover from loss • some redundancy may exist in order to give improved access time or simpler address methods • harmful redundancy • cost of storing multiple copies • necessary to update multiple copies • system may be inconsistent when in different stages of updating

6. DATABASE SYSTEMS • Constant Growth - a data base is not a static entity • to allow for change over time, with possible restructuring of the physical data. • new data and applications may be added • data independence

7. DATABASE SYSTEMS • Logical data independence • the overall logical structure of the data may be changed without changing the application programs. • The changes must not, of course, remove any of the data the application programs use.)

8. DATABASE SYSTEMS • Physical data independence • the physical layout and organization of the data may be changed without changing either the overall logical structure of the data or the application programs.

9. DATABASE SYSTEMS • Data Views • External View • View of data from a partiular program. • Multiple views may exist for multiple needs • Conceptual View • Complete discription of data stored • Internal View • Physical organization of actual data

10. DATABASE SYSTEMS • Conceptual View • While the programmer's view of data change and the physical storage and organization change, the conceptual model remains stable or grows to incorporate more data types. • Describes the entire set fields and relationships in the data • Called the schema

11. DATABASE SYSTEMS • Conceptual View • The Schema is the underlying view of the data, from which all external views can be derived • A well designed conceptual model will only need to grow, a badly designed model will have to be modified and changed later.

12. DATABASE SYSTEMS • External View • Each use of the data may require a different external view • Permits access to subsets of the data • Security - some data is hidden, readonly • Flexibility - schema changes shouldn't affect programs • Understanding - programers and users need not understand the complexities of the underlying data

13. DATABASE SYSTEMS • Internal View • Only the database management system need know this • indexes, file structures, access techniques, etc. • DB administrator may modify parameters for performance.

14. DATABASE SYSTEMS • The Objectives of a Data-Base organization • The ultimate objective is to make application development easier, cheaper, faster, and more flexible. • A data-base should be a repository of the data needed for an organization data processing. • The conceptual view should reflect the "true properties of the data."

15. DATABASE SYSTEMS • Primary Objectives of Data-Base Organization • The Data Base is the Foundation Stone of Future Application Development • It should make application development easier, cheaper, faster and more flexible. • The Data Can Have Multiple Uses • Different users who perceive the same data differently can employ them in different ways. • Intellectual Investment is Protected • Existing programs and logical data structures (representing many man-years) will not have to be redone when changes are made to the data base.

16. DATABASE SYSTEMS • Primary Objectives of Data-Base Organization • Clarity • Users can easily know and understand what data are available to them. • Ease of Use • Users can gain access to data in a simple fashion. • Complexity is hidden from the users by the data-base management system. • Flexible Usage • The data can be used or searched in flexible ways with different access paths.

17. DATABASE SYSTEMS • Primary Objectives of Data-Base Organization • Unanticipated Requests for Data Can Be Handled Quickly • Spontaneous requests for data can be handled without application programs having to be written (a time-consuming bottleneck), by means of high-level query or report generation languages. • Change Is Easy • The data base can grow and change without interferring with established ways of using the data. • Low Cost • Low cost of storing and using data, and minimization of the high cost of making changes.

18. DATABASE SYSTEMS • Primary Objectives of Data-Base Organization • Less Data Proliferation • New application needs may be met with existing data rather creating new files. • Performance • Data request can be satisfied with speed suitable to the usage of the data. • Accuracy and Consistency • Accuracy controls will be used. • The system will avoid having multiple versions of the same data item available to users in different stages of updating.

19. DATABASE SYSTEMS • Primary Objectives of Data-Base Organization • Protection from Loss or Damage • Privacy • Unauthorized access to the data will be prevented. • The same data may be restricted in different ways from different uses. • Data will be protected from failures and catastrophes, and from criminals, vandals, incompetents, and persons who might falsely update them. • Availability • Data are quickly available to users at almost all times when they need them.

20. DATABASE SYSTEMS • Secondary Objectives (to help achieve the primary objectives) • Physical Data Independence • Storage hardware and physical storage techniques can be changed without causing application program rewriting. • Logical Data Independence • New data items can be added, or the overall logical structures expanded, without existing programs having to be rewritten. • Controlled Redundancy • Data items will be stored only once except where there are technical or economic reasons for redundant storage.

21. DATABASE SYSTEMS • Secondary Objectives • Suitably Fast Access • Access mechanisms and addressing methods will be fast enough for the usage in question. • Suitably Fast Searching • The need for fast spontaneous searching of the data will grow as interactive systems usage spreads. • Data Standardization Within a Corporation • Interdepartmental agreement is needed on data formats and definitions. • Standardization is needed between departments who would otherwise have created incompatible data.

22. DATABASE SYSTEMS • Secondary Objectives • Data Dictionary • A data dictionary, defining all data items used, is needed. • High-level Programmer Interface • Application programmers should use simple, powerful data requests and be insulated from the complexities of file layout and addressing. • End User Language • A high-level query or report-generation language should permit some end users to bypass the application programming step.

23. DATABASE SYSTEMS • Secondary Objectives • Integrity Controls • Range checks and other controls should detect data inaccuracies where possible. • Fast Recovery from Failures • Automatic recovery without loss of transactions. • Tunability • The data base should be tunable, to improve performance without causing application program rewriting.

24. DATABASE SYSTEMS • Secondary Objectives • Design and Monitoring Aids • Aids which permit the designer of data administrator to predict and optimize performance. • Automatic Reorganization or Migration • Data migration or other automatic physical reorganization designed to improve performance. • Evolution to Distributed Data Base Operation • The system should be designed so that distributed processing and computer network operations can evolve.