Computer Science 202-CH6-DBdesign

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Barry Irwin August 2003

Barry Irwin August 2003 Rhodes University CS202 : DatabasesRhodes University CS202 : Databases 11

Computer Science 202 Computer Science 202

Database Systems:

Database Design Database Design

2 2 Barry Irwin August 2003

Barry Irwin August 2003 Rhodes University CS202 : DatabasesRhodes University CS202 : Databases

Objectives Objectives

To learn what an information system is.

To learn what a Database Life Cycle To learn what a Database Life Cycle (DBLC) is.

(DBLC) is.

To learn what a Systems Development To learn what a Systems Development Life Cycle (SDLC) is.

Life Cycle (SDLC) is.

To demonstrate the relationship between To demonstrate the relationship between the DBLC and the SDLC.

the DBLC and the SDLC.

To learn how database design fits into the To learn how database design fits into the design of an information system.

design of an information system.

Data

Data vs. Information Information

Data Data

n

Raw facts stored in a database Raw facts stored in a database

n

Little to no meaning in isolation Little to no meaning in isolation

n

Require organisation in order to be useful Require organisation in order to be useful Information

Information

n

Used for decision making Used for decision making

n

Result of a transformation of data Result of a transformation of data

n

Consists of data processed and organised in Consists of data processed and organised in a useful way

a useful way – – e.g. tables, graphs e.g. tables, graphs

The Information System The Information System

A system containing a repository of data, A system containing a repository of data, which is able to process the data and which is able to process the data and produce informational output

produce informational output

Manages data collection, storage and Manages data collection, storage and retrieval

retrieval

Also consists if the people and processes Also consists if the people and processes related to the management of data related to the management of data

Data processing Data processing

Systems Analysis Systems Analysis

Systems Analysis

Systems Analysis is the process that is the process that establishes the need for and the extent of a establishes the need for and the extent of a Information System

Information System

The process of creating an information system is The process of creating an information system is Systems Development

Systems Development

Database design and development are an Database design and development are an integral part of the systems development integral part of the systems development process

process

Systems development follows a lifecycle (SDLC)

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Systems Development Life Cycle Systems Development Life Cycle

SDLC SDLC

Planning Planning Analysis Analysis

Detailed systems design Detailed systems design Implementation

Implementation Maintenance Maintenance

SDLC

SDLC - - Planning Planning

Planning of the project Planning of the project Definition of

Definition of

n n

Scope Scope

n n

Budget Budget

n

Resources Resources

SDLC

SDLC - - Analysis Analysis

Break down the project into manageable Break down the project into manageable components

components

Identify specifics regarding components Identify specifics regarding components Gather Requirements

Gather Requirements

SDLC

SDLC – –Detailed Design Detailed Design

In detail specification of In detail specification of

n

HCI components HCI components

n

Data structures Data structures

n n

API API

n

Internal Component functionality Internal Component functionality Testing Framework designed Testing Framework designed

SDLC

SDLC - - Implementation Implementation

Implementation of the System Implementation of the System

Can be on a component by component Can be on a component by component level (eXtreme Programming)

level (eXtreme Programming)

Implementation includes development of Implementation includes development of

n

Test harnesses Test harnesses

n

Unit Tests Unit Tests

n

System Tests System Tests

(3)

SDLC

SDLC – – Maintenance Maintenance

Corrective process Corrective process

Remedy errors found in testing Remedy errors found in testing Iterative

Iterative

Can also follow post deployment Can also follow post deployment

DB Development Lifecycle DB Development Lifecycle

DBLC DBLC

Initial study Initial study Database Design Database Design

n

Conceptual Design Conceptual Design

Data analysis Data analysis

ERD construction and data normalisation ERD construction and data normalisation Data model verification

Data model verification ER Verification ER Verification

n

DBMS software selection DBMS software selection

n

Logical Design Logical Design

n

Physical Design Physical Design

Implementation and Loading Implementation and Loading Testing and evaluation Testing and evaluation Operation

Operation

Maintenance and Evaluation Maintenance and Evaluation

DBLC

DBLC – – Initial Design Initial Design

Analyse company situation Analyse company situation

n

Current Operating environment Current Operating environment

n

Organisational Structure Organisational Structure

n

Information Flow Information Flow Define the problem Define the problem

Define scope and constraints of project Define scope and constraints of project Define design objectives

Define design objectives

DBLC Initial Design DBLC Initial Design

DBLC

DBLC – – DB DESIGN DB DESIGN

Database Design Database Design

n

Conceptual Design Conceptual Design

n

DBMS software selection DBMS software selection

n

Logical Design Logical Design

n

Physical Design Physical Design

Critical part of whole process Critical part of whole process Focus on the Data requirements Focus on the Data requirements Final design should satisfy the Final design should satisfy the requirements

requirements

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DBLC

DBLC – – DB DESIGN DB DESIGN

DBLC

DBLC – – DB DESIGN DB DESIGN Conceptual Conceptual

Develop a high

Develop a high- -level abstraction of the level abstraction of the data model

data model

Conceptual Design consists of four distinct Conceptual Design consists of four distinct parts

parts

Data analysis Data analysis

ERD construction and data normalisation ERD construction and data normalisation Data model verification

Data model verification ER Verification ER Verification

Data Analysis and Requirements Data Analysis and Requirements

Focus on:

n

Information needs Information needs

n

Information users Information users

n

Information sources Information sources

n

Information constitution Information constitution Data sources

Data sources

n

Developing and gathering end Developing and gathering end- -user data views user data views

n

Direct observation of current system Direct observation of current system

n

Interfacing with systems design group Interfacing with systems design group Business rules

Business rules

Entity Relationship Entity Relationship Modeling and Normalization Modeling and Normalization

E

E- - R Modeling is Iterative R Modeling is Iterative

Figure 6.8

Concept Design: Tools and Concept Design: Tools and

Sources

(5)

Data Model Verification Data Model Verification

E

E- - R model is verified against proposed system R model is verified against proposed system processes

processes

n

End user views and required transactions End user views and required transactions

n

Access paths, security, concurrency control Access paths, security, concurrency control

n

Business Business- -imposed data requirements and constraints imposed data requirements and constraints Reveals additional entity and attribute details Reveals additional entity and attribute details Define major components as modules Define major components as modules

n

Cohesively Cohesively

n

Coupling Coupling

E

E- - R Model Verification Process R Model Verification Process

Iterative Process of Iterative Process of

Verification Verification

Figure 6.10

Distributed Database Design Distributed Database Design

Design portions in different physical Design portions in different physical locations

locations

Development of data distribution and Development of data distribution and allocation strategies

allocation strategies

DBLC

DBLC – – DB DESIGN DB DESIGN Software Selection Software Selection

Selection of the correct software is critical Selection of the correct software is critical For possible candidates, both advantages For possible candidates, both advantages and disadvantages need to be compared and disadvantages need to be compared Common influencing factors:

Common influencing factors:

n

Cost Cost – – purchase and ongoing support purchase and ongoing support

n

DBMS features and management tools DBMS features and management tools

n

Hardware/Platform requirements Hardware/Platform requirements

n

Underlying Model ( e.g.. OOD , RD) Underlying Model ( e.g.. OOD , RD)

DBLC

DBLC – – DB DESIGN DB DESIGN Logical Design Logical Design

Process of converting the conceptual model into Process of converting the conceptual model into an appropriate form for the DBMS chosen an appropriate form for the DBMS chosen Maps conceptual objects to logical DB Maps conceptual objects to logical DB constructs ( tables and relations) constructs ( tables and relations) Common components:

Common components:

n n

Tables Tables

n n

Indexes Indexes

n n

Views Views

n

Access Control Access Control

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DBLC

DBLC – – DB DESIGN DB DESIGN Physical Design Physical Design

Physical layout of data on partitions Physical layout of data on partitions Highly technical

Highly technical

Can have an big impact on performance Can have an big impact on performance Most designers favour transparency of Most designers favour transparency of physical layout

physical layout

Complicated on distributed systems Complicated on distributed systems

Physical Design Physical Design

DBLC

DBLC - - Implementation and Implementation and Loading

Loading

Creation of special storage

Creation of special storage- -related constructs related constructs to house end

to house end- -user tables user tables Data loaded/imported into tables Data loaded/imported into tables Other issues to be considered Other issues to be considered

n

Performance Performance

n n

Security Security

n

Backup and recovery Backup and recovery

n n

Integrity Integrity

n

Company standards Company standards

n

Concurrency controls Concurrency controls

DBLC

DBLC - - Testing and evaluation Testing and evaluation

Database is tested and fine

Database is tested and fine- -tuned against a tuned against a number of criteria, including

number of criteria, including

n

performance, integrity, concurrent access security performance, integrity, concurrent access security constraints

constraints

Done in parallel with application development Done in parallel with application development Corrective actions taken to correct problems:

Corrective actions taken to correct problems:

n

Fine Fine- -tuning based on reference manuals tuning based on reference manuals

n

Modification of physical design Modification of physical design

n

Modification of logical design Modification of logical design

n

Upgrade or change DBMS software or hardware Upgrade or change DBMS software or hardware

DBLC

DBLC - - Operation Operation

Database considered operational Database considered operational

‘Go

‘Go- -live’ procedures live’ procedures

Possible running in parallel with old systems Possible running in parallel with old systems Starts process of system evaluation Starts process of system evaluation Unforeseen problems may surface Unforeseen problems may surface

Demand for change is constant and must be Demand for change is constant and must be managed

managed

Importance of adherence to the original Importance of adherence to the original specification.

specification.

DBLC

DBLC - - Maintenance and Maintenance and Evaluation

Evaluation

Preventative maintenance Preventative maintenance Corrective maintenance Corrective maintenance Adaptive maintenance Adaptive maintenance

Assignment of access permissions Assignment of access permissions Generation of database access statistics to Generation of database access statistics to monitor performance

monitor performance

Periodic security audits based on system Periodic security audits based on system - - generated statistics

generated statistics Periodic system usage

Periodic system usage- -summaries summaries

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Design Strategies Design Strategies

Top Top- -down down

n

Identify the data sets Identify the data sets

n

Define the data elements Define the data elements

Bottom Bottom- -up up

n

Identify data elements Identify data elements

n

Group elements into data sets Group elements into data sets

Design Strategies Design Strategies

Centralised vs. Decentralised Centralised vs. Decentralised

Design Design

Centralized design Centralized design

n

Typical of simple databases Typical of simple databases

n

Conducted by single person or small team Conducted by single person or small team Decentralized design

Decentralized design

n

Larger numbers of entities and complex Larger numbers of entities and complex relations

relations

n

Spread across multiple sites Spread across multiple sites

n

Developed by teams Developed by teams

Decentralised

Decentralised Design Design