Systems Development Systems Development Life Cycle Life Cycle A simplified introduction

You will need to take notes throughout the presentation

Stages of the CycleStages of the Cycle

1. Problem definition2. Feasibility study3. Analysis4. Design5. Implementation6. Maintenance

Why do we need the Why do we need the SDLC?SDLC?The software crisis of the late

‘60s and early ‘70s Systems were delivered years

lateThey were over budgetUnreliableDifficult to maintainDid not do what was required

What does the SDLC do?What does the SDLC do?Systems Development Life Cycle

was an attempt to establish a structured approach to systems development.

For management, each stage of the life cycle was a milestone with an associated date and set of deliverables.

DeliverablesDeliverablesEach stage has an associated set

of deliverablesSets of documents produced at

each stage in the life cycle

1. Problem Definition1. Problem DefinitionThe problem definition forms the

basis of the problems and requirements list (see later)

It records all problems and requirements mentioned by clients in interviews, or which are subsequently discovered during analysis of the system.

Problem Definition Report – Problem Definition Report – the purposethe purposeTo provide a written statement of

the user's current problems and requirements; to get agreement with the user.

To ensure that the right problem is being tackled

To force the user to become involved

To define the current state of the system and the required end state

Problem Definition Report – Problem Definition Report – the sectionsthe sectionsProblemObjectivesScopePreliminary ideasRecommended action

2. Feasibility Study2. Feasibility Study Feasibility study - is there a practical solution to the

problem outlined in the initial problem definition.

In particular, the feasibility study examines the technical, financial and organisational feasibility of the project:

◦ Can it be done?

◦ Can we afford it?

◦ Will the proposed new system fit in with existing procedures?

Feasibility study report

◦ Presented by the system developer to the user

◦ Decision is made whether or not to proceed.

3. Analysis3. AnalysisDeliverable from the analysis stage is the

‘Specification of requirements’Logical model of the required systemStates WHAT the system is to doSays nothing about HOW to implement it Includes

◦ Data flow diagrams◦ Data dictionary◦ Process definitions◦ E/R model◦ Entity life histories or state diagrams

4. Design4. Design

This has two stages:Provides several different

solutions to the problemSelects one solution and specifies

it in detail

Design – Alternative Design – Alternative solutionssolutionsA very cheap solution which does

the job and no more.A medium price solution which

does the job well and is convenient for the user;

A high cost, all-singing, all dancing solution

How solutions may differHow solutions may differSystem boundaries; Automation boundaries; could

remain manual.HardwareSoftwareDesign strategiesUser interfaceCosts

Design – Selecting a Design – Selecting a solutionsolutionSpecification may include:Program design (e.g. structure

charts) and specificationSpecification of the user

man/machine interface Specification of the layout of

reports and other system outputs File and record specificationsHardware specifications,

including costsImplementation schedule

5. Implementation5. ImplementationProgram listings, test plans and

supporting documentationManual of operating proceduresManual of clerical proceduresUser manualHardware on which the system will

runThe system must be installed at the

clients' site on their equipment Changeover from the old to the new

system supervised Often a hand-holding period

6. Maintenance6. MaintenanceStarts as soon as the system is

handed overTerm maintenance often

euphemism for finding and correcting errors

True maintenance is modifying the system to meet evolving client requirements

System developer must start again at the beginning of the cycle

An example, simplified An example, simplified systemsystem

The System RequirementsThe System Requirements

BackgroundBackgroundErrors in requirements may account

for approximately 50 per cent of the total cost of debugging a software system.

Many of the traditional system development methods merely pay lip service to identifying, describing and validating the client’s requirements for the system.

Today requirements engineering is recognised as a crucial stage in the development of software.

Requirements – what are Requirements – what are they?they?No consensus of opinion as to what

is meant by requirementsSystem requirements - the

client’s needs and wishes. Software requirements -

constraints put on the system development, such as hardware, software and design methods.

Requirements EngineeringRequirements Engineering

Covers three phases:elicitation (identifying

requirements)specification (describing them in

an appropriate language or notation)

validation (checking with the client that the description accurately records his or her needs and wishes).

Different types of Different types of requirementsrequirementsFunctional requirements: what the

system has to do what its inputs and outputs are and how these are linked.

Non-functional requirements: the attributes of the system as it performs its job; can be divided into 1. non-functional requirements of the system

and2. non-functional requirements arising from

external sources.

Non-functional System Non-functional System RequirementsRequirementsUsabilityPerformanceReliability Security

ElicitationElicitation

This covers several different activities:

Observation of the users at workStudy of relevant documentsUser questionnairesTalking to the people involved in

the system

The Requirements The Requirements SpecificationSpecificationA cornerstone of a system

development projectEncapsulates the shared

understanding and intentions of all the stakeholders

May be used as a vehicle for communication between developers, users and other stakeholders

The Requirements The Requirements SpecificationSpecificationMay form the basis of a legal

contract between developer and client

Guides the programmers in their implementation of the system

Desirable qualities of a requirements specification can be found in the IEEE Recommended Practice for Software Requirements Specifications from the IEEE Standard 831–1993.

Requirements ValidationRequirements ValidationTechnically feasible to confirm that

the requirements specification document is of the desired quality

Not easy to ascertain whether the requirements expressed in the specification are really what the client wants and needs

The client may not know what he or she wants

Requirements ValidationRequirements ValidationPrototyping allows the client and

users to get some feeling for how their ideas would work once implemented in a computer system.

Talk through the requirement specification with the client and users.

SummarySummaryStage Stage ContentContent DeliverableDeliverable

1.1. Problem DefinitionProblem Definition What is the problem?What is the problem? Problem Definition Report - statement of Problem Definition Report - statement of problems, scope and objectives problems, scope and objectives

objectives of new systemobjectives of new system

2.2. Feasibility Study Feasibility Study Is there a feasible Is there a feasible solution – quick look solution – quick look ahead to see if you can ahead to see if you can do something about the do something about the

problemproblem

Feasibility Study Report - rough cost benefit Feasibility Study Report - rough cost benefit analysisanalysis

- system scope and objectives cost benefit - system scope and objectives cost benefit analysisanalysis

3. Analysis3. Analysis What What must be done to must be done to solve the problemsolve the problem

Specification of Requirements –logical Specification of Requirements –logical model of required systemmodel of required system

4.4. DesignDesign HowHow should the problem should the problem be solvedbe solved

Technical Design Specification –includes Technical Design Specification –includes program specifications, hardware program specifications, hardware specifications, cost estimates and an specifications, cost estimates and an implementation scheduleimplementation schedule

5.5. ImplementationImplementation Do itDo it Working system, includes program listings and Working system, includes program listings and documentation, test plan, hardware, operating documentation, test plan, hardware, operating procedures, clerical proceduresprocedures, clerical procedures

6.6. MaintenanceMaintenance Modify system as Modify system as necessarynecessary

Working system - Operational system, modified Working system - Operational system, modified and documented as requiredand documented as required

TasksTasksUsing one or two A4 sides, list

each stage of the SDLC, using illustrations and diagrams where appropriate

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