Lesson I. Database Management Systems

Transcription

1 Lesson I Database Management Systems

2 IN THIS LESSON YOU WILL LEARN The concept and importance of information. What an information system is and its components. The structure of data files and the drawbacks of filebased system. What a database is and the advantages of using a database management system. The meaning of data model and a list of the main data models in use. The three layer architecture for databases. The different users of a database. 2

3 1. Information 2. Information Systems 3. File-based IS 4. Database Management Systems (DBMS) 5. Data Modelling 6. ANSI/SPARK Architecture

4 Information

5 1. INFORMATION 1.1 Introduction 1.2 Importance 1.3 Information vs Computer Science 1.4 Quality of Information 1.5 Properties of Information

6 INFORMATION Introduction Nowadays, the amount of information we are exposed to is huge. e.g: weather prediction, horoscopes, train timetable... All areas of human development need to manipulate information. This information is changing constantly. 6

7 Why is information so important?

8 INFORMATION Importance In our society the information has become a very important resource. Relevant and timely information is essential to make decisions. In addition, all organisations need to save and access data. 8

9 INFORMATION Information vs Computer Science In Catalan and Spanish the term computer science comes from the French word: information automatique informatique 9 That is what we are interested in!!

10 INFORMATION Information vs Data Data are the record of facts. It can be only series of numbers or characters with no meaning. Information implies that the data have been processed so that they mean something for the recipient. 10

11 Activity 1.1 Information vs Data

12 INFORMATION Quality of Information Information is considered high-quality if it permits the recipient to make the best decision. The quality of the information is more important than its quantity. There are a set of properties that allow you to assess the quality of the information. 12

13 INFORMATION Properties of Information - relevant - accurate - complete - transmitted to the right person - reported in time - understandable - up to date - reliable to the user - safe It s not possible to get all of them!! 13

14 Activity 1.2 Quality of Information

15 1. Information 2. Information Systems 3. File-based IS 4. Database Management Systems (DBMS) 5. Data Modelling 6. ANSI/SPARK Architecture

16 Information Systems

17 2. INFORMATION SYSTEMS 2.1 Concept 2.2 Components 2.3 Connection between Components and Objectives 2.4 Analysis and Design 2.5 Automated Information Systems

18 INFORMATION SYSTEMS Concept Companies and organisations have an infrastructure that allows the information to be manipulated quickly and easily. Organisation s INFORMATION SYSTEM (IS) 18

19 INFORMATION SYSTEMS Components An information system is made up of: information users physical support working procedures Can you guess what each of these 19 components is?

20 Who decides on the information system?

21 2. INFORMATION SYSTEMS Components 2.3 Information Users Physical Suport Working Procedures

22 INFORMATION SYSTEMS Information It s the most important component of the systems. Which information must be stored? 22

23 2. INFORMATION SYSTEMS Components 2.3 Information Users Physical Suport Working Procedures

24 INFORMATION SYSTEMS Users People that insert, manipulate or use the information to carry out their tasks. Who is manipulating the information? 24

25 2. INFORMATION SYSTEMS Components 2.3 Information Users Physical Suport Working Procedures

26 INFORMATION SYSTEMS Physical Support All devices used to communicate, process and store information. Which physical elements will be used to manipulate the information? 26

27 Are computers part of the physical supports in all IS?

28 INFORMATION SYSTEMS Physical Support It s possible to find information systems that only use basic tools to manipulate information. Nowadays computers have replaced those old tools. Although they are not essential!! 28

29 INFORMATION SYSTEM Physical Support 29 data file

30 INFORMATION SYSTEM Physical Support We are interested in IS that do use computers to manipulate information. 30

31 INFORMATION SYSTEMS Physical Support 31

32 INFORMATION SYSTEMS Physical Support The database systems are the heart of all current IS because they allow to manage large amounts of data. 32

33 2. INFORMATION SYSTEMS Components 2.3 Information Users Physical Suport Working Procedures

34 INFORMATION SYSTEMS Working Procedures The IS must help to achieve the general objectives of the company. So, the managers decide a set of working guidelines that they consider more efficient and useful. How should things be done? 34

35 INFORMATION SYSTEMS Connection between Components and Objectives The working procedures determine the: necessary information involved users necessary physical support 35

36 INFORMATION SYSTEMS Connection between Components and Objectives The working procedures also have to adapt to the available elements: information characteristics of the users existing technology 36

37 Activity 1.3 What is the role of a database expert in a nonautomated IS?

38 INFORMATION SYSTEMS 38

39 INFORMATION SYSTEMS Analysis and Design databases application programs 39 information system

40 Activity 1.4 Identifying the components of an IS

41 INFORMATION SYSTEMS Automated Infomation Systems An automated IS is made up of the following elements: information working procedures users software hardware Is it the only physical support used? administrator 41

42 1. Information 2. Information Systems 3. File-based IS 4. Database Management Systems (DBMS) 5. Data Modelling 6. ANSI/SPARK Architecture

43 File-based Information Systems

44 3. FILE-BASED IS s 3.1 Files 3.2 Concept 3.3 Separate Application Programs 3.4 Drawbacks 3.5 Database

45 FILE-BASED INFORMATION SYSTEMS Files The computer s RAM memory is volatile. The file is a high-level structure provided by the operating system that keeps the data in mass storage. Different types of files store different types of information. We are interested in data files and database files. 45

46 FILE-BASED INFORMATION SYSTEMS Concept Data files are used to store the information. In the same company or organisation, there are several programs that perform services for the final users. Each program defines and manages its own data. 46

47 FILE-BASED INFORMATION SYSTEMS Separate Application Programs 47

48 SEPARATE PROGRAMS Example Consider two departments in our college: - admissions office - personnel Both of them need to keep information about the teachers but the information required is slightly different. 48

49 SEPARATE PROGRAMS Example This approach has several limitations!! 49

50 FILE-BASED INFORMATION SYSTEMS Drawbacks - Data dependence - Incompatible file formats - Security problems - Data redundancy What are these disadvantages about? 50

51 FILE-BASED IS DRAWBACKS Data Dependence If some modifications have to be made in the data, then the application program has to be rewritten. 51

52 FILE-BASED IS DRAWBACKS Incompatible File Formats The structure of the file depends on the application programming language. e.g. the structure of the files generated by C and Visual Basic may be different. o The incompatibility of such files makes it difficult to process them together. 52

53 FILE-BASED IS DRAWBACKS Security Problems There are no mechanisms to control the different permissions on the users. In case of a system crash it also becomes hard to recover the data to a consistent state. 53

54 3. FILE-BASED IS s 3.4 Drawbacks Data Dependence Incompatible File Formats Security Problems Data Redundancy

55 FILE-BASED INFORMATION SYSTEMS Data Redundancy Data redundancy means duplication of data. Data redundancy leads to: - wastage of storage space - more laborious updating process - loss of data integrity!! 55

56 LOSS OF DATA INTEGRITY Example Let s imagine that one of the teachers moves to another address: BUT.. Files with contradictory information!! 56

57 What of the previous disadvantages is the worst?

58 To solve the problems mentioned before... database systems A database is a well-organised collection of data that is related in a meaningful way. 58

59 How do database systems solve the problems mentioned?

60 DATABASE Definition All the data needed by the organisation are in the database. All users access a single place to get the information they need. 60

61 DATABASE Integrated Information 61

62 1. Information 2. Information Systems 3. File-based IS 4. Database Management Systems (DBMS) 5. Data Modelling 6. ANSI/SPARK Architecture

63 Database Management Systems

64 4. DBMS 4.1 Concept 4.2 Data Access 4.3 Advantages 4.4 DBMS vs File-based Systems 4.5 Drawbacks 4.6 Elements 4.7 Languages 4.8 Users

65 DATABASE MANAGEMENT SYSTEM Concept A DBMS is a collection of programs that permits the user to create and manipulate databases. The DBMS provides the interface between the database and the programs that access the data. 65 Do you know any DBMS? e.g: Access, MySQL, Oracle, Postgress,...

66 DBMS Data Access 66

67 What are the advantages of having all the data in a single place?

68 DBMS Advantages - Data dependence - Incompatible file formats - Security problems - Data redundancy - Data independence - Data standardization - Security tools - Controlled redundancy 68

69 ADVANTAGES DBMS Data Independence Data independence means independence between application program and data. When the data representation changes, it is not necessary to change the application program. 69

70 ADVANTAGES DBMS Data Standardisation There s a greater degree of data standardization within the organisation. The users are obliged to use the same data definitions. 70

71 ADVANTAGES DBMS Controlled Redundancy Since the data are recorded only once: data need less space the data updating process is easier there s no data inconsistency!! 71

72 ADVANTAGES DBMS Security Utilities Access to data can be restricted so that only authorised users may see or manipulate it. Backup copies of data need to be made regularly to recover in case of system failure. 72

73 4. DBMS 4.3 Advantages Data Independence Data Standardisation Controlled Redundancy Security Utillities 4.4 DBMS vs File-based Systems

74 DBMS DBMS vs File-based Systems FILE-BASED SYSTEM Data dependence Incompatible file formats Data redundancy Security problems DBMS SYSTEM Data independence Data standardization Controlled redundancy Backup and recovery utilities Restricted authorized access 74

75 Activity 1.5 Advantages of a DBMS

76 Is there any disadvantage of using a DBMS?

77 DBMS Disadvantages The enterprise may be assuming additional risks in the following areas: the cost of using DBMS data integrity data quality confidentiality, privacy and security enterprise vulnerability 77

78 Activity 1.6 Disadvantages of a DBMS

79 What can you do with a DBMS?

80 DBMS Elements A practical database package tipically provides utilities for: 80 - Design and maintenance of database structures - Formulation of queries - Design of forms - Design of reports - Contruction of macros and programs

81 DBMS Languages The DBMS has languages and procedures to communicate with the database. Data Definition Language (DDL) Data Manipulation Language (DML) What is the purpose of these 81 languages?

82 DBMS LANGUAGES Data Definition Language It operates on the data structures. It is used to: - define a database - modify its structure - destroy it when you no longer need it 82

83 DBMS LANGUAGES Data Manipulation Language It operates on the data. There are four things that you can do with data: store the data change the stored data remove data from the database retrieve data from a database 83

84 Activity 1.7 DBMS Languages

85 DBMS Users A database involves a group of people: database designer database users database administrator What are these people in charge of? 85

86 USERS OF A DBMS Database Designer The database designer is responsible for: Identifying the data to be stored in the database. Choosing an appropriate structure to represent and store the data. 86

87 USERS OF A DBMS Database Administrator The objectives of DBA are: - To control the access to the database - To restore a consistent state of the database from a system failure - To standardize the use of databases - To support the development and maintenance of database application programs - To ensure all the documentation is up-to-date 87

88 USERS OF A DBMS Database Users They are people who need information from the database to carry out their tasks. Database users Application programmers: Write application programs and interact with the database through a host language like Pascal or C End users - Specialized end users - Non-experienced final users 88

89 1. Information 2. Information Systems 3. File-based IS 4. Database Management Systems (DBMS) 5. Data Modelling 6. ANSI/SPARK Architecture

90 Data Modelling

91 5. DATA MODELLING 5.1 Concept of Modelling 5.2 Why Modelling? 5.3 Meaning of Data Modelling 5.4 Advantages 5.5 Difficulties

92 MODELLING Concept A model of something is a representation that shares certain relevant features with the original. e.g. An actual physical scale model A musical score A plan of a house A set of equations Can you give examples of models? 92

93 Why modelling?

94 MODELLING Why Modelling? Models are useful because the characteristics of the real system can be analysed by studying the nature and behaviour of the model. Models can give an accurate description. There s no ambiguity!! 94

95 DATA MODELLING Meaning We need techniques that allow us to represent a conceptual view of the information involved in information systems. Data models are also concerned about the processing of data and the definition of operations on these. 95

96 DATA MODELLING Meaning The real system to be modelled usually refers to a company or organisation. 96

97 DATA MODELLING Advantages The use of data models provides a better understanding of the nature of information. They enable a better design of database systems. 97

98 DATA MODELLING Difificulties One difficulty in data modelling is the difference between the human view of an IS and the way it has to be implemented within the computer. To solve this, we can view the architecture of a database as a series of levels that provide different degrees of abstraction. 98

99 1. Information 2. Information Systems 3. File-based IS 4. Database Management Systems (DBMS) 5. Data Modelling 6. ANSI/SPARK Architecture

100 ANSI/SPARK Architecture

101 6. ANSI/SPARK ARCHITECTURE 6.1 Concept 6.2 Levels of Abstraction 6.3 Logical Level 6.4 Pysical Level 6.5 Schemas 6.6 Types of Data Models 6.7 Data Independence

102 ANSI/SPARC DATA MODEL Concept Proposed by ANSI/SPARC for database systems. The data in a DBMS is represented at three levels of abstraction. There s a schema at each of these levels. A schema is the structure of the database, described in a formal language supported by the DBMS. 102

103 ANSI/SPARC DATA MODEL Levels of Abstraction 103

104 ANSI/SPARK DATA MODEL To do this we need... DATA MODELS 104

105 DATA MODELS Types There is a large number of data models: Hierarchical Model Network Model Relational Model Entity-Relationship Model Object-Oriented model

106 ANSI/SPARC DATA MODEL Levels of Abstraction 106

107 ANSI/SPARC DATA MODEL Logical Level The reality of the information system is represented to obtain a conceptual schema. From this schema, it s described what data are stored. The logical schema contains the organisation of the data into tables and columns. 107

108 ANSI/SPARC DATA MODEL ER model Relational model 108

109 ANSI/SPARK DATA MODEL Physical Level It describes how the data relations described in the conceptual schema will be physically stored using a particular DBMS. 109

110 ANSI/SPARC DATA MODEL External Level It is the highest level of abstraction. An external schema is the view that the individual user of the database has. Users are not allowed to access all the information in the database 110

111 LOGICAL LEVEL Conceptual Schema The real-world information system is represented to obtain a conceptual schema. 111

112 CONCEPTUAL SCHEMA Example 112 Entity-relationship diagram

113 LOGICAL LEVEL Logical Schema From this schema, it s described what data are stored. The logical schema contains the organisation of the data into rows and columns. 113

114 LOGICAL SCHEMA Example TEACHER (id, name, address ) SUBJECTS (code, name, hours, id_teacher) foreign key: id_teacher TEACHERS Relational Model 114

115 LOGICAL SCHEMA Example TEACHER (id, name, address ) SUBJECTS (code, name, hours, id_teacher) foreign key: id_teacher TEACHERS tables id name address 12 Fox BCN 25 McKewan BCN 80 Fox GRN code name hours id_teacher C1 OS C2 NET C3 DB TEACHERS 115 SUBJECTS

116 DATA MODELS Types SCHEMA Conceptual Schema (real-world) Logical Schema (data description) Internal Schema (implementation of tables) MODEL Entity-Relationship model (ERM) -Relational model -Hierarchical model -Network model 116

117 DATA MODELS Hierarchical Model Formed the basis of the earliest databases. Organised data were arranged on a top-down structure. 117

118 DATA MODELS Network Model It was a more general representation of the hierachical model with no distiction between parent and child. 118

119 DATA INDEPENDENCE Data independence means that the changes in the way the data are structured and stored don t affect the programs. Physical data independece Logical data independence 119

120 DATA INDEPENDENCE Physical Data Independence It is the ability to modify physical schema without causing the conceptual schema or application programs to be rewritten. 120

121 DATA INDEPENDENCE Physical Independence PHYSICAL INDEPENDENCE 121

122 DATA INDEPENDENCE Logical Data Independence It s the ability to modify the conceptual schema without having to change the external schemas or application programs. 122

123 DATA INDEPENDENCE Physical vs Logical Data Independence LOGICAL INDEPENDENCE 123

124 DATA INDEPENDENCE Physical vs Logical Data Independence LOGICAL INDEPENDENCE PHYSICAL INDEPENDENCE 124