Chapter 2 · 3 Chapter 2 - Objectives Purpose/importance of conceptual modeling. Typical functions and services a DBMS should provide. Function and importance of system catalog. Software

1

Chapter 2

Database Environment

Pearson Education © 2009

2

Chapter 2 - Objectives

Purpose of three-level database architecture.

Contents of external, conceptual, and internal levels.

Purpose of external/conceptual and conceptual/internal mappings.

Meaning of logical and physical data independence.

Distinction between DDL and DML.

A classification of data models.


3

Chapter 2 - Objectives

Purpose/importance of conceptual modeling.Typical functions and services a DBMS should provide.Function and importance of system catalog.Software components of a DBMS.Meaning of client–server architecture and advantages of this type of architecture for a DBMS.Function and uses of Transaction Processing Monitors.


4

Objectives of Three-Level Architecture

All users should be able to access same data.

A user’s view is immune to changes made in other views.

Users should not need to know physical database storage details.


5

Objectives of Three-Level Architecture

DBA should be able to change database storage structures without affecting the users’ views.

Internal structure of database should be unaffected by changes to physical aspects of storage.

DBA should be able to change conceptual structure of database without affecting all users.


6

ANSI-SPARC Three-Level Architecture


7


External Level– Users’ view of the database. – Describes that part of database that is

relevant to a particular user.

Conceptual Level– Community view of the database. – Describes what data is stored in database

and relationships among the data.


8


Internal Level– Physical representation of the database on

the computer. – Describes how the data is stored in the

database.


9

Differences between Three Levels of ANSI-SPARC Architecture


10

Data Independence

Logical Data Independence– Refers to immunity of external schemas to

changes in conceptual schema.– Conceptual schema changes (e.g.

addition/removal of entities).– Should not require changes to external

schema or rewrites of application programs.


11

Data Independence

Physical Data Independence– Refers to immunity of conceptual schema to

changes in the internal schema.– Internal schema changes (e.g. using different

file organizations, storage structures/devices).– Should not require change to conceptual or

external schemas.


12

Data Independence and the ANSI-SPARC Three-Level Architecture


13

Database Languages

Data Definition Language (DDL)– Allows the DBA or user to describe and

name entities, attributes, and relationships required for the application

– plus any associated integrity and security constraints.


14

Database Languages

Data Manipulation Language (DML)– Provides basic data manipulation operations

on data held in the database.Procedural DML – allows user to tell system exactly how to

manipulate data.Non-Procedural DML – allows user to state what data is needed

rather than how it is to be retrieved.Fourth Generation Languages (4GLs)


15

Data Model

Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization.

Data Model comprises:– a structural part;– a manipulative part;– possibly a set of integrity rules.


16

Data Model

Purpose– To represent data in an understandable way.

Categories of data models include:– Object-based– Record-based– Physical.


17

Data Models

Object-Based Data Models– Entity-Relationship– Semantic– Functional– Object-Oriented.

Record-Based Data Models– Relational Data Model– Network Data Model– Hierarchical Data Model.

Physical Data ModelsPearson Education © 2009

18

Relational Data Model


19

Network Data Model


20

Hierarchical Data Model


21

Conceptual Modeling

Conceptual schema is the core of a system supporting all user views.Should be complete and accurate representation of an organization’s data requirements.

Conceptual modeling is process of developing a model of information use that is independent of implementation details.Result is a conceptual data model.


Enterprise Data ModelEnterprise Data Model

•• First step in database developmentFirst step in database development•• Specifies scope and general contentSpecifies scope and general content•• Overall picture of organizational data at high Overall picture of organizational data at high

level of abstractionlevel of abstraction•• EntityEntity--relationship diagramrelationship diagram•• Descriptions of entity typesDescriptions of entity types•• Relationships between entitiesRelationships between entities•• Business rulesBusiness rules

22

23

Figure 2-1 Segment from enterprise data model

Enterprise data model describes the high-level entities in an organization and the relationship between these entities

Information EngineeringInformation Engineering•• A dataA data--oriented methodology to create and oriented methodology to create and

maintain information systemsmaintain information systems•• TopTop--down planningdown planning––a generic IS planning a generic IS planning

methodology for obtaining a broad methodology for obtaining a broad understanding of the IS needed by the entire understanding of the IS needed by the entire organizationorganization

•• Four steps to TopFour steps to Top--Down planning:Down planning:–– PlanningPlanning–– AnalysisAnalysis–– DesignDesign–– ImplementationImplementation

24

25

Identify Strategic Planning Factors Identify Strategic Planning Factors (Table 2(Table 2--2)2)

•• Organization goalsOrganization goals––what we hope to what we hope to accomplishaccomplish

•• Critical success factorsCritical success factors––what MUST work what MUST work in order for us to survivein order for us to survive

•• Problem areasProblem areas––weaknesses we now haveweaknesses we now have

26

Identify Corporate Planning Objects Identify Corporate Planning Objects (Table 2(Table 2--3)3)

•• Organizational unitsOrganizational units––departmentsdepartments•• Organizational locationsOrganizational locations•• Business functionsBusiness functions––groups of business groups of business

processesprocesses•• Entity typesEntity types––the things we are trying to the things we are trying to

model for the databasemodel for the database•• Information systemsInformation systems––application programsapplication programs

27

Develop Enterprise ModelDevelop Enterprise Model

•• Functional decompositionFunctional decomposition–– Iterative process breaking system description Iterative process breaking system description

into finer and finer detailinto finer and finer detail•• Enterprise data model Enterprise data model

•• Planning matrixes Planning matrixes –– Describe interrelationships Describe interrelationships

between planning objectsbetween planning objects

28

29

Planning MatrixesPlanning Matrixes

•• Describe relationships between planning Describe relationships between planning objects in the organizationobjects in the organization

•• Types of matrixes:Types of matrixes:–– LocationLocation--toto--functionfunction–– UnitUnit--toto--functionfunction–– ISIS--toto--data entitydata entity–– Supporting functionSupporting function--toto--data entitydata entity–– ISIS--toto--business objectivebusiness objective

30

Example Business FunctionExample Business Function--toto--Data Data Entity Matrix (Fig. 2Entity Matrix (Fig. 2--3)3)

31

Two Approaches to Database and Two Approaches to Database and IS DevelopmentIS Development

•• SDLCSDLC–– System Development Life CycleSystem Development Life Cycle–– Detailed, wellDetailed, well--planned development processplanned development process–– TimeTime--consuming, but comprehensiveconsuming, but comprehensive–– Long development cycleLong development cycle

•• PrototypingPrototyping–– Rapid application development (RAD)Rapid application development (RAD)–– Cursory attempt at conceptual data modelingCursory attempt at conceptual data modeling–– Define database during development of initial prototypeDefine database during development of initial prototype–– Repeat implementation and maintenance activities with Repeat implementation and maintenance activities with

new prototype versionsnew prototype versions

32

Systems Development Life CycleSystems Development Life Cycle(see also Figures 2.4, 2.5) (see also Figures 2.4, 2.5)

33

Planning

Analysis

Physical Design

Implementation

Maintenance

Logical Design

Systems Development Life CycleSystems Development Life Cycle(see also Figures 2.4, 2.5) (cont.)(see also Figures 2.4, 2.5) (cont.)

34

Planning

Analysis

Physical Design

Implementation

Maintenance

Logical Design

Planning Purpose––preliminary understandingDeliverable––request for study

Database activity––enterprise modeling and early conceptual data modeling

Systems Development Life CycleSystems Development Life Cycle(see also Figures 2.4, 2.5) (cont.) (see also Figures 2.4, 2.5) (cont.)

35

Planning

Analysis

Physical Design

Implementation

Maintenance

Logical Design

Analysis

Purpose–thorough requirements analysis and structuringDeliverable–functional system specifications

Database activity–thorough and integrated conceptual data modeling


36

Planning

Analysis

Physical Design

Implementation

Maintenance

Logical DesignLogical Design

Purpose–information requirements elicitation and structureDeliverable–detailed design specifications

Database activity–logical database design (transactions, forms, displays, views, data integrity and security)


37

Planning

Analysis

Physical Design

Implementation

Maintenance

Logical Design

Physical Design

Purpose–develop technology and organizational specificationsDeliverable–program/data structures, technology purchases, organization redesigns

Database activity–physical database design (define database to DBMS, physical data organization, database processing programs)


38

Planning

Analysis

Physical Design

Implementation

Maintenance

Logical Design

Implementation

Purpose–programming, testing, training, installation, documentingDeliverable–operational programs, documentation, training materials

Database activity–database implementation, including coded programs, documentation, installation and conversion


39

Planning

Analysis

Physical Design

Implementation

Maintenance

Logical Design

Maintenance

Purpose–monitor, repair, enhanceDeliverable–periodic audits

Database activity–database maintenance, performance analysis and tuning, error corrections

40

Prototyping Database MethodologyPrototyping Database Methodology(Figure 2.6) (Figure 2.6)

41

Prototyping Database MethodologyPrototyping Database Methodology(Figure 2.6) (Figure 2.6) (cont.)(cont.)

42

Prototyping Database MethodologyPrototyping Database Methodology(Figure 2.6)(Figure 2.6) (cont.)(cont.)

43

Prototyping Database MethodologyPrototyping Database Methodology(Figure 2.6)(Figure 2.6) (cont.)(cont.)

44

Prototyping Database MethodologyPrototyping Database Methodology(Figure 2.6) (Figure 2.6) (cont.)(cont.)

CASECASE•• ComputerComputer--Aided Software Engineering Aided Software Engineering

(CASE)(CASE)––software tools providing automated software tools providing automated support for systems developmentsupport for systems development

•• Three database features:Three database features:–– Data modelingData modeling––drawing entitydrawing entity--relationship relationship

diagramsdiagrams–– Code generationCode generation––SQL code for table creationSQL code for table creation–– RepositoriesRepositories––knowledge base of enterprise knowledge base of enterprise

informationinformation

45

Packaged Data ModelsPackaged Data Models•• Model components that can be purchased, Model components that can be purchased,

customized, and assembled into fullcustomized, and assembled into full--scale data scale data modelsmodels

•• AdvantagesAdvantages–– Reduced development timeReduced development time–– Higher model quality and reliabilityHigher model quality and reliability

•• Two types:Two types:–– Universal data modelsUniversal data models–– IndustryIndustry--specific data modelsspecific data models

46

Managing ProjectsManaging Projects•• ProjectProject––a planned undertaking of related a planned undertaking of related

activities to reach an objective that has a activities to reach an objective that has a beginning and an endbeginning and an end

•• Involves use of review points for:Involves use of review points for:–– Validation of satisfactory progressValidation of satisfactory progress–– Step back from detail to overall viewStep back from detail to overall view–– Renew commitment of stakeholdersRenew commitment of stakeholders

•• Incremental commitmentIncremental commitment––review of systems review of systems development project after each development development project after each development phase with rejustification after each phasephase with rejustification after each phase

47

Managing Projects: People InvolvedManaging Projects: People Involved

•• Business analystsBusiness analysts•• Systems analystsSystems analysts•• Database analysts and data modelersDatabase analysts and data modelers•• UsersUsers•• ProgrammersProgrammers•• Database architectsDatabase architects•• Data administratorsData administrators•• Project managersProject managers•• Other technical expertsOther technical experts

48

Database SchemaDatabase Schema•• External SchemaExternal Schema

–– User ViewsUser Views–– Subsets of Conceptual SchemaSubsets of Conceptual Schema–– Can be determined from businessCan be determined from business--function/data entity function/data entity

matricesmatrices–– DBA determines schema for different usersDBA determines schema for different users

•• Conceptual SchemaConceptual Schema–– EE--R modelsR models––covered in Chapters 3 and 4covered in Chapters 3 and 4

•• Internal Schema Internal Schema –– Logical structuresLogical structures––covered in Chapter 5covered in Chapter 5–– Physical structuresPhysical structures––covered in Chapter 6covered in Chapter 6

49

50

Different people have different views of the database…these are the external schema

The internal schema is the underlying design and implementation

Figure 2-7 Three-schema architecture

51

52

Pine Valley FurniturePine Valley Furniture

53

Segment of project data model (Figure 2-11)

54

Figure 2-12 Four relations (Pine Valley Furniture)

55

Figure 2-12 Four relations (Pine Valley Furniture) (cont.)

56

Functions of a DBMS

Data Storage, Retrieval, and Update.

A User-Accessible Catalog.

Transaction Support.

Concurrency Control Services.

Recovery Services.


57

Functions of a DBMS

Authorization Services.

Support for Data Communication.

Integrity Services.

Services to Promote Data Independence.

Utility Services.


58

System Catalog

Repository of information (metadata) describing the data in the database.One of the fundamental components of DBMS.Typically stores:– names, types, and sizes of data items;– constraints on the data;– names of authorized users;– data items accessible by a user and the type of

access;– usage statistics.


59

Components of a DBMS


60

Components of Database Manager (DM)


61

Multi-User DBMS Architectures

Teleprocessing

File-server

Client-server


62

Teleprocessing

Traditional architecture.Single mainframe with a number of terminals attached.Trend is now towards downsizing.


63

File-Server

File-server is connected to several workstations across a network.Database resides on file-server.DBMS and applications run on each workstation.Disadvantages include:– Significant network traffic.– Copy of DBMS on each workstation.– Concurrency, recovery and integrity control more

complex.


64

File-Server Architecture


65

Traditional Two-Tier Client-Server

Client (tier 1) manages user interface and runs applications.Server (tier 2) holds database and DBMS.Advantages include:– wider access to existing databases;– increased performance;– possible reduction in hardware costs;– reduction in communication costs;– increased consistency.


66



67



68

Three-Tier Client-Server

Client side presented two problems preventing true scalability:– ‘Fat’ client, requiring considerable resources on

client’s computer to run effectively.– Significant client side administration overhead.

By 1995, three layers proposed, each potentially running on a different platform.


69


Advantages: – ‘Thin’ client, requiring less expensive hardware.– Application maintenance centralized. – Easier to modify or replace one tier without

affecting others. – Separating business logic from database functions

makes it easier to implement load balancing. – Maps quite naturally to Web environment.


70



71

Transaction Processing Monitors

Program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for Online Transaction Processing (OLTP).


72

TPM as middle tier of 3-tier client-server


Documents

Chapter 2 · 3 Chapter 2 - Objectives Purpose/importance of conceptual modeling. Typical functions and services a DBMS should provide. Function and importance of system catalog. Software