Lecture 2

System Development Lifecycles

Building a house Definition phase Analysis phase Design phase Programming phase System Test phase Acceptance phase Operation phase

Lifecycles System Development Lifecycles

covers the whole life of a system technical products

Project Lifecycles delivery of a specified product technical products, quality products,

management products

Development Lifecycle Models Waterfall Model

“b” Model “V” Model Incremental Model Traditional Approach Structured Method

SSADM Spiral Model

Waterfall Model Feature

a number of sequential stages a degree of iteration of work and

products within a stage very little iteration between stages rework is carried in succeeding stages

Waterfall Model Advantage

sequencing of activities quality management

verification validation

configuration management

Waterfall Model Disadvantage

planning, control and risk management are not covered

Application requirements are well understood not likely to undergo significant

business change

“ b” Model Feature

variation of the waterfall model it takes its name from its distinctive “b”

shape maintenance and enhancement shown as a

series of cycles each of which follows the same general sequence as the original development

Advantage maintenance phase is adequately covered

“ V” Model Feature

variation of the waterfall model the successive stages are shown in a

“V” format shows correspondence between the

different stages of the project

“ V” Model Advantage

demonstrates elements of quality assurance in its treatment of the correspondence

Application development work being provided by

external contracts

Incremental Model Feature

variation of waterfall model phased delivery

Advantage delivery and testing more

manageable allowing familiarization with the

changes

Incremental Model Disadvantage

difficult to break the delivery of system down into phases

introduce overheads of integration Application

total scope and definition of requirements must be completed before the increments are defined.

Spiral Model Feature

an evolutionary or iterative approach to systems development

project starts at the center of the spiral and progress outwards

at the center, the requirements will be poorly understood and will be successively refined with each rotation around the spiral

Spiral Model the total cost of the project will

increase as the length of the spiral increases

four quadrants top left quadrant top right quadrant bottom right quadrant bottom left quadrant

Spiral Model Advantage

objective setting, risk management & planning

Application requirements are not well formed or

understood by the users difficult to specify the requirements difficult to determine how a proposed

solution will perform in practice

Traditional Approach Feature

unstructured and non-specific variations of the waterfall model

Advantage analyst can use “intuitive” methods of

working limited demands on the user’s time documentation was relatively easy to

understand, being mostly in English

Traditional Approach Disadvantage

lack of user involvement poor quality abdication of responsibility by the users

and blame for the developers use of text-based

ambiguous and misunderstanding emphasis on how rather than what

Structured Methods Feature

have largely taken over the traditional approach in the development of IS projects

offer a set of techniques and tools to carry out the systems development work within a defined framework

Structured Methods Advantage

user involvement separation of logical and physical emphasis on data diagrammatic documentation defined structure

Structured Methods Disadvantage

users and analysts/developers need to be trained to understand the documentation

amount of time required from users will be much increased

lead to increased level of documentation and therefore of bureaucracy

disastrous to assume that the method, rather than the analyst, will do the work

SSADM Structured Systems Analysis and Design

Method Three basic views of an information

system what information is stored and how it is

interrelated Logical Data Structure

how information is passed around Data Flow Diagrams

how information is changed during its lifetime Entity Life Histories

SSADM Combines techniques into a well-

established framework, provide alternative views of a system that cross-check each other to ensure that an accurate and complete picture of the system is formed

Overview of SSADM Information systems planning

strategic planning for the development of future and existing information systems

partial SSADM support Project Initiation

project is set up, terms of reference agreed, team members assigned, and plans drawn up

full SSADM support

Overview of SSADM Feasibility study

decided whether project is technically possible, whether it can be financially and socially justified, and whether the new system will be accepted by the organization

full SSADM support

Overview of SSADM Systems analysis

Analyze the current system and determine the requirements for a new system

full SSADM support Business systems design

Detailed logical design of the new system is developed in a non-technical way

full SSADM support

Overview of SSADM Physical design

convert logical design to physical design that fits the computer hardware and software selected

full SSADM support Construction

programming, the assembly of programs into a system and testing

partial SSADM support

Overview of SSADM Transition

transition from operating the old system to operating the new

partial SSADM support Production

completely handed over to the users no SSADM support

Overview of SSADM Maintenance and review

correction of errors, adaptation to new software and hardware releases, and minor enhancements

Partial SSADM support

Principles of SSADM Structures

define the frameworks of steps and stages and their inputs and outputs

stage 1 : analysis of system operations and current problems

stage 2 : specification of requirements stage 3 : selection of technical options stage 4 : logical data design stage 5 : logical process design stage 6 : physical design

Principles of SSADM Techniques

define how the steps and tasks are performed

diagrammatic techniques Data Flow Diagrams Logical Data Structures Entity Life Histories Logical Dialogue Design

Principles of SSADM non-diagrammatic techniques

relational data analysis first cut rules physical design control quality assurance project estimating

Principles of SSADM Documentation

defines how the products of the steps are presented

documents diagrams forms matrices narrative reports