1. 14. Databases

2. DATABASEMANAGEMENTSYSTEMDATABASEMANAGEMENTSYSTEM 14.1

3. D BMS components  A database is a collection of data that is logically, but not necessarily physically, coherent.  A database management system (DBMS) defines, creates, and maintains a database and allows controlled access to users.

4. ARCHITECTUREARCHITECTURE 14.2

5. D atabase architecture

6.  DBMS users can be humans or application programs.  A DBMS has three levels: internal, conceptual, and external.  The internal level of a DBMS interacts directly with the hardware and is concerned with low-level access methods and byte transfer to and from the storage device.  The conceptual level of a DBMS defines the logical view of the data as well as the data model and schema diagrams.  The external level of a DBMS interacts directly with the user.

7. DATABASEMODELSDATABASEMODELS 14.3

8. D atabase models  A database model defines the logical design of data  The model also describes the relationships between different parts of data.  Three models:  Hierarchical model  Network model  Relational model

9. H ierarchical model  Data are organized as an upside down tree  Each entity has only one parent but can have several children.

10. N etwork model  The entities are organized in a graph, where some entities can be accessed through several path.

11. RELATIONALMODELRELATIONALMODEL 14.4

12. R elational model  Data are organized in two-dimensional tables called relations.  The relational database management system (RDBMS) is the only database model in wide use today. The hierarchical and network models are obsolete.  Each column in a relation is called an attribute. The number of attributes in a relation is its degree.  Each row in a relation is called a tuple. The number of rows in a relation is its cardinality.

13. R elational model

14. R elation

15. OPERATIONSONRELATIONSOPERATIONSONRELATIONS 14.5

16. I nsert operation  None operations can be performed on relations.  An operation that operates on one relation is a unary operator. Unary operators include the insert, delete, update, select, and project operations.

17. D elete operation

18. U pdate operation

19. S elect operation

20. P roject operation

21. J oin operation  An operation that operates on two relation is a binary operator. binary operators include the join, union, intersection, and difference operations.

22. U nion operation

23. I ntersection operation

24. D ifference operation

25. STRUCTUREDQUERYLANGUAGESTRUCTUREDQUERYLANGUAGE 14.6

26. S QL  The Structured Query Language (SQL) is the language standardized by ANSI and ISO for use on relational databases.  For example: Fig 14.10Fig 14.10 select* 整個 tuple 都抓出來 fromCOURSES whereUnit = 5

27. S QL - S QL - cont ’ s For example: selectCourse- Name fromCOURSES whereUnit = 5