1. Database and Database Users
Database Systems
Chapter 1
Database and Database Users
主講人:陳建源
研究室 :法401
日期:99/9/28

2. Outline Introduction Characteristics of the Database Approach
Actors on the Scene
Workers behind the Scene
A Brief History of Database Applications
When Not to Use a DBMS

3. 1. Introduction Basic Definitions Database Data
A collection of related data
Data
Known facts that can be recorded and have an implicit meaning
Mini-world (Universe of Discourse, UoD)
Some part of the real world about which data is stored in a database
E.g., student grades and transcripts at a university

4. 1. Introduction Database Management System (DBMS) Database System
A software package/ system to facilitate the creation and maintenance of a computerized database
Database System
The DBMS software together with the database
Sometimes, the applications are also included
Defining a database
Specify the data types, structures, and constraints of the data to be stored

5. 1. Introduction Meta-data Manipulating a database
Database definition or descriptive information
Stored by the DBMS in the form of a database catalog or dictionary
Manipulating a database
Query and update the database miniworld
Generate reports

6. 1. Introduction Sharing a database Application program Query
Allow multiple users and programs to access the database simultaneously
Application program
Accesses database by sending queries to DBMS
Query
Causes some data to be retrieved

7. 1. Introduction Transaction Protection includes:
May cause some data to be read and some data to be written into the database
Protection includes:
System protection
Security protection
Maintain the database system
Allow the system to evolve as requirements change over time

8. 1. Introduction

9. 1. Introduction Example of a Database
Mini-world for the example: Part of a UNIVERSITY environment
Some mini-world entities
STUDENTs
COURSEs
SECTIONs (of COURSEs)
(academic) DEPARTMENTs
INSTRUCTORs

10. 1. Introduction Some mini-world relationships
SECTIONs are of specific COURSEs
STUDENTs take SECTIONs
COURSEs have prerequisite COURSEs
INSTRUCTORs teach SECTIONs
COURSEs are offered by DEPARTMENTs
STUDENTs major in DEPARTMENTs

11. 1. Introduction

12. 1. Introduction Phases for designing a database:
Requirements specification and analysis
Conceptual design
Logical design
Physical design

13. 2. Characteristics of Database Approach
Database v.s. File-processing
Self-contained nature
A DBMS catalog stores the description of the database (called meta-data)
This allows the DBMS software to work with different databases
Program-data independence
Allows changing data storage structures and operations without having to change the DBMS access programs

14. 2. Characteristics of Database Approach
For example, a STUDENT record
If add another field, Birthday
File-processing: needs to rewrite the program
Database system: only change the STUDENT description, no change to DBMS program

15. 2. Characteristics of Database Approach
Data abstraction
A data model is used to hide storage details and present the users with a conceptual view of the database
Support of multiple views of the data
Each user may see a different view of the database, which describes only the data of interest to that user
A view may be materialized (stored) or virtual (definition)

16. 2. Characteristics of Database Approach
Different database views reveal different combinations of data

17. 2. Characteristics of Database Approach
Student transcript view
Course prerequisite view

18. 2. Characteristics of Database Approach
Sharing of Data and Multiuser Transaction Processing
Allow multiple users to access the database at the same time
The DBMS must include concurrency control software (On-line transaction processing,OLTP)
e.g., Air-line reservation
is an executing program or process

19. 2. Characteristics of Database Approach
Additional Advantages
Controlling redundancy
In file-processing approach, every user group
maintains its own files
e.g., Course registration, Accounting office
Problems: inconsistency, wasted storage
In database approach, all user groups are
integrated, no redundancy
But in some cases, redundancy is useful; need redundancy controlling to prohibit inconsistency
例如mirror設計可加快查詢

20. 2. Characteristics of Database Approach
Controlled redundancy
Uncontrolled redundancy

21. 2. Characteristics of Database Approach
Enforcing integrity constraints
Data type constraint
e.g., Grade: A, B, C, D, E
Relationship constraint
e.g., every section record is related to a course record
Uniqueness constraint
e.g., CourseNumber
Note: errors may occur even if integrity constraints
hold
e.g., a student’s grade A is wrongly entered C

22. 2. Characteristics of Database Approach
Restricting unauthorized access
Sharing of data among multiple users
Providing multiple user interfaces
Representing complex relationships
Providing backup and recovery
Potential for enforcing standards
Reduced application development time
Flexibility to change data structures

23. 2. Characteristics of Database Approach
Availability of up-to-date information
Economies of scale

24. 3. Actors of Database Systems
Database administrators (DBA) are responsible for:
Authorizing access to the database
Coordinating and monitoring its use
Acquiring software and hardware resources
Database designers are responsible for:
Identifying the data to be stored
Choosing appropriate structures to represent and store this data

25. 3. Actors of Database Systems
End users
People whose jobs require access to the database
Types
Casual end users
Naive or parametric end users
Sophisticated end users
Standalone users

26. 3. Actors of Database Systems
System analysts
Determine requirements of end users
Application programmers
Implement these specifications as programs

27. 4. Workers behind the Scene
DBMS system designers and implementers
Design and implement the DBMS modules and interfaces as a software package
Tool developers
Tools are optional packages, e.g., GUI
Operators and maintenance personnel
Responsible for the actual running and maintenance

28. 5. A Brief History of Database Applications
Early database applications using hierarchical and network systems
Large numbers of records of similar structure
Providing data abstraction and application flexibility with relational databases
Separates physical storage of data from its conceptual representation
Provides a mathematical foundation for data representation and querying

29. 5. A Brief History of Database Applications
Object-oriented applications and the need for more complex databases
Used in specialized applications: engineering design, multimedia publishing, and manufacturing systems
Interchanging data on the Web for e-commerce using XML
Extended markup language (XML) primary standard for interchanging data among various types of databases and Web pages

30. 5. A Brief History of Database Applications
Extending database capabilities for new applications
Extensions to better support specialized requirements for applications
Enterprise resource planning (ERP)
Customer relationship management (CRM)
Databases versus information retrieval
Information retrieval (IR)
Deals with books, manuscripts, and various forms of library-based articles

31. 6. When not to use a DBMS Main costs of using a DBMS
High initial investment and possible need for additional hardware
Generality that a DBMS provides for defining and processing data
Overhead for providing generality, security, recovery, integrity, and concurrency control

32. 6. When not to use a DBMS When a DBMS may be unnecessary
The database and applications are simple,
well defined, and not expected to change
There are stringent real-time requirements that may not be met because of DBMS overhead
Multiple-user access to data is not required

33. Summary Database DBMS Several categories of database users
Collection of related data (recorded facts)
DBMS
Generalized software package for implementing and maintaining a computerized database
Several categories of database users
Database applications have evolved
Current trends: IR, Web