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Information Systems Development (ISD)

Systems Development Life CycleOverview of Analysis PhaseOverview of Design Phase

CP2236: Information Systems Design

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Information Systems Development (ISD)

A logical series of development phases followed in an organisation to conduct all the steps necessary to analyse, design, implement & maintain information systems.

These logical series of development phases - known as System Development Life Cycle (SDLC).

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Systems Development Life Cycle (SDLC)

•Waterfall Model

– Proven approach

– Lacks flexibility

– Time lag

– Ensures points of review

Feasibility

Analysis

Design

Implement

Maintain

Review

Time

Scope & objectives

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Feasibility

Analysis

Design

Maintain

Review

Alternative Approaches (1)

•Waterfall SDLC with iterations:

Implement

Scope & objectives

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Alternative Approaches (2)

• Beer mat and hack.

• Prototyping / Rapid Application Development.– Uses a different SDLC– System developed in smaller units– Iterative– Less time lag– User participation

Analysis

Design

Code

Review

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Alternative Approaches (4)Spiral model includes best features of both the classic Waterfall SDLC and the Prototyping approach.

PlanningRisk Analysis

DevelopmentEvaluation

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Alternative Approaches (5)

Each spiral consists of four main activities:

• Planning: setting project objectives; defining alternatives; further planning on the next spiral; etc.

• Risk Analysis: analysis of alternatives & the identification & solution of risks.

• Development: designing, coding and testing etc. in increments.

• Evaluation: user evaluation of each spiral and then the final product.

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SDLC Stages and Deliverables (1)

Feasibility

Scope & Objectives

Analysis

Design

Terms of Reference

Feasibility Report

Requirement specification, Physical & Logical models

Logical models of required system, physical design and detailed design documentation

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Implementation:Code, Test & Install

Maintain

Review

Code - program documentationTest - Test plans from unit to system & acceptance testingInstall - system changeover, installation of hw/sw, user & system documentation and training

Maintenance procedures

Evaluation report

SDLC Stages and Deliverables (2)

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Analysis - Overview (1)

Feasibility

Design

MaintainReview

Time

PRL RC current system’s DFDs LDS I/Os Process desc.

RequirementsSpecificationof req.System

Analysis

Implement

Scope & Objectives

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Analysis - Overview (2)

Current Physical

DFDs

Current LogicalDFDs

Current System

LDS

Problem Requirements

List (Requirements

Catalogue)Logicalisation

Data Store Entity Cross Reference

PHYSICAL ANALYSIS

LOGICAL ANALYSIS

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• Analysis - gathering & documentation of information about the current system & the required system.

• To achieve this - a number of techniques are used.

– Problem Requirement List feeds into Requirements Catalogue: contain information about current problems & future requirements

(logical: functional & physical: non-functional)

– Data Flow Diagrams (Processing): contain information about the processing, inputs and outputs and data stores to be accessed.

Analysis - Overview (3)

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Analysis - Overview (4)– Logical Data Structures (Data): contain

information about the groups of data (entities) and their relationships.

– Input\Output Descriptions: contain information about data that flows into and out of the system.

– Process Descriptions: contain information about how the processes actually work & these can be specified using various techniques (e.g. Structured English, Decision Tables & Decision Trees).

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Analysis - Physical & Logical

• Physical analysis includes all physical aspects– e.g. Filing cabinets, Locations, (Who, When,

Where, etc).

• Physical analysis become logical when all the physical aspects are removed by logicalisation.– Therefore there are 2 versions of the DFDs current

physical and current logical.

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Analysis - Data & Processing

• DFDs model information about the processing in the current system.

• LDS models information about the data in the current system.

• Data & Processing are two separate but essential components of an Information System.

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Analysis - Techniques

• The techniques used to perform analysis are taken from Structured Systems Analysis and Design Methodology (SSADM).

• There are other techniques and ways of combining them in order to perform analysis.

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Design - Overview (1)

FeasibilityAnalysis

MaintainReview

Time

DesignImplement

Scope & Objectives

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Design - Overview (2)

Design

RequirementsSpecificationof req. System

PRL RC current system’s DFDs LDS I/Os Process desc.

SystemSpecificationof req. System

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Design - Overview (3)

Design

RequiredPhysical Design

Required Logical Design

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Design - Overview (4)

Logical Design: gives a detailed logical definition of the required system.

Physical Design: takes the products of the logical design and produces specifications for the target hardware and software.

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Design - Overview (5)

Logical Design: •No reference made to any technical environment.

•Capable of implementation on a variety of platforms.

•Act as a model of how the system will satisfy the user requirements.

•Reflect underlying business rules & activities rather than physical constraints.

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Design - Overview (6)

Logical Design - blueprint is the delivered product of the required system. It includes the following:• Requirements Catalogue• Required system DFDs• Required system LDS• Relational Data Analysis (normalised set

of tables and rationalised set of tables)

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Design - Overview (7)

Physical Design: •Logical design translated into a physical design based on the technical environment selected, e.g. platform, programming language, database etc.

•Produces program specifications, physical files or database definitions and user interfaces for a selected target hardware & software.

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Design - Overview (8)

Physical design includes contents of the following components;

• Data design - (requirements for data to be stored in a database)

• Outputs design - (reports, displays)• Inputs design - (forms, screens, dialogues)• Programs design - (structure of programs to

collect, transform & output data)

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Design Overview (9)

DESIGNI/O

Descriptions

Interface Design

Data Design

Program Design

Systemchangeoverstrategies

Documentation:System & User

Requirements Catalogue

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Physical and Logical Models

Current Physical

Current Logical

Required Logical

RequiredPhysical

Analysis Design