1 1 Chapter 1 Introduction to Database Management Database Management. - презентация

1 1 1 Chapter 1 Introduction to Database Management Database Management

2 2 1 Objectives u Provide a general introduction to the field of database management u Introduce basic terminology u Describe the advantages and disadvantages of database processing u Provide a brief history of database management u Describe the hierarchical and network database models

3 3 1 Introduction u Chapter uses the example of Henry, the owner of four bookstores u Current file system is difficult and costly to use u Interested in different categories of data, called entities, including books, authors, publishers, and branches, and the relationships between these entities

4 4 1 Henrys Basic Data u File - an organized collection of data about a single entity u Record - pertains to a specific person, place, thing, or event u Fields - contain certain facts about that specific person, place, thing, or event

5 5 1 Figure 1.1 Branch File

6 6 1 Figure 1.2 Publisher and Author Files

7 7 1 Figure 1.3 Book File

8 8 1 Figure 1.4 Book-Author and Book-Branch Files

9 9 1 Using a Database Management System (DBMS) u A DBMS is a program or collection of programs whose function is to manage a database on behalf of the people who use it. u Database design is the determination of the structure of the database.

10 10 1 Figure 1.5 Branch Form

11 11 1 Figure 1.6 Book Form

12 12 1 Figure 1.7 Book Report

13 13 1 Figure 1.8 Main Switchboard

14 14 1 Figure 1.9 Maintain Data Switchboard

15 15 1 Entities, Attributes, and Relationships u Entity – a person, place, thing, or event u Attribute – a property of an entity l For the entity Person, attributes could include eye color and height u Relationship – an association between entities l Publishers are related to the books they publish, and a book is related to its publisher

16 16 1 Figure 1.10 Entities and Attributes

17 17 1 Figure 1.11 One-to-Many Relationship

18 18 1 Files and Databases u Data file – stores information on a single entity and the attributes of that entity u Database – a structure that can store information about multiple types of entities, the attributes of these entities, and the relationships among the entities

19 19 1 Database Management System (DBMS) u DBMS programs manipulate databases either for the user, or a program the user is executing u Mainframe DBMSs have been used since the 1960s u Since the mid-1980s, DBMSs on PCs possess many of the features of their mainframe counterparts

20 20 1 Figure 1.12 Using Database Management Systems

21 21 1 Database Processing u Database processing – the data to be processed are stored in a database and the data in the database are being manipulated by the DBMS u Nondatabase approach l Duplication of data l Extremely difficult to fulfill requirements that involve data from more than one system

22 22 1 Figure 1.13 Nondatabase Approach

23 23 1 Database Processing u Database approach l Common database managed by a DBMS l Each entity appears only once in the system, reducing the duplication of data l With all data being in a single database, it is possible to list all information concerning the entities

24 24 1 Figure 1.14 Database Approach

25 25 1 Figure 1.15 Advantages of Database Processing

26 26 1 Advantages of Database Processing u Getting more information from the same amount of data l When all the data for various systems are stored in a single database, the information becomes available, as well as the process of retrieving the information can be quick and easy

27 27 1 Advantages of Database Processing u Sharing of data l Several users can have access to the same piece of data u Balancing conflicting requirements l A person or group, often called Database Administration/Administrator (DBA) can structure the database in such a way that it benefits the entire organization, not just a single group

28 28 1 Advantages of Database Processing u Controlling redundancy l Not only saves space, but makes the updating process easier u Consistency l Consistency is a direct result of redundancy, so by reducing redundancy, there is much less potential for this sort of inconsistency with the database approach

29 29 1 Advantages of Database Processing u Integrity l An integrity constraint is a rule that must be followed by data in the database u Example: Not allowing a persons age to be lower than zero u Security l The prevention of access to the database by unauthorized users

30 30 1 Advantages of Database Processing u Increasing productivity l A good DBMS comes with many features that allow users to gain access to data without having to do any programming at all u Data independence l A property that allows the structure of a database to be changed without the programs that access the database having to change

31 31 1 Figure 1.16 Disadvantages of Database Processing

32 32 1 Disadvantages of Database Processing u DBMS size l DBMSs are large programs that occupy a large amount of disk space as well as internal memory u DBMS complexity l The complexity and breadth of the functions provided by a DBMS make it a complex product to use

33 33 1 Disadvantages of Database Processing u Greater impact of a failure l A failure on the part of any one user that damages the database in some way may affect all the other users on the system u More difficult recovery l If the database is being updated by a large number of users, all updates must be redone since the time of its restoration

34 34 1 History of Database Management u IBM developed the Generalized Update Access Method (GUAM) in 1964 for North American Rockwell, the prime contractor for the APOLLO project u GUAM was made available for the general public under the name Data Language/I (DL/I) in 1966

35 35 1 History of Database Management u DL/I became the data management component for the Information Management System (IMS), which was the dominant DBMS for many years u In the mid-1960s, General Electric developed Integrated Data Store (I-D-S)

36 36 1 History of Database Management u The COnference on DAta SYstems Languages (CODASYL) tackled the problem of providing standards for DBMSs in the late 1960s u In 1971, the CODASYL standards were presented to the American National Standards Institute (ANSI)

37 37 1 History of Database Management u Throughout the 1970s, the relational model was the subject of intense research u The 1980s is when the first commercial relational DBMSs appeared u The 1980s saw the development of object-oriented database management systems (OODBMSs)

38 38 1 Hierarchical and Network Databases u Four types of data models l Network l Hierarchical l Relational l Object-oriented

39 39 1 Network Model u Perceived by the user as a collection of record types and relationships between these record types u I-D-S and other CODASYL systems are examples of DBMSs that conform to the network data model

40 40 1 Figure 1.17 Network Database Structure

41 41 1 Hierarchical Model u Perceived by the user as a collection of hierarchies, or trees u More restrictive structure than a network model u GUAM, DL/I, and IMS are examples of DBMSs that conform to the hierarchical model

42 42 1 Figure 1.18 Hierarchical Database Structure