The systems life cycle
Large systems development projects can take several years to develop and can be extremely
costly. It is important that projects are delivered on time, within budget and meet the required
specification. To this end most commercial organisations follow the systems life cycle approach
to developing systems. The systems life cycle consists of a series of well-defined stages, which
when followed, prevent large projects from developing in a haphazard fashion.
The systems life cycle
Problem definition
Feasibility
Study
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Analysis
Design
Programming/development
Installation/implementation
Maintenance
The stages in systems development
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The waterfall model
The waterfall model is a variation on the systems life cycle model. As the project develops
analyst/programmers often find flaws in the design and so earlier stages have to be redeveloped.
The waterflow model reflects this by having arrows that go up and down the model
Analysis
Feasibility Study
Requirements Analysis
Design
Implementation
Design
Coding and testing
Conversion
Review and
Maintenance
PostImplementation review
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The stages in systems development
Problem definition
The problem domain is defined by investigations being made to identify the problems with current
system; for example, a manual system may be in operation in which large volumes of data are
being repetitively processed. The investigation begins by thoroughly understanding the present
system. A fact-finding approach is employed. In order to understand the system a number of
techniques can be employed, such as flowcharts , structure charts. When the new requirements
are analysed and a new system is proposed.
The User Request (problem domain) is the first step in the systems development cycle, it will
involve Formal/informal discussions between users/management and the analyst. A Formal
document called the Terms of Reference is produced and consists of :
The Terms of Reference:
1) Objectives what the new system must achieve, these include quantifiable and unquantifable
(tangible) benefits e.g cost reductions, better service to customers, better management
information, ability to handle increased volumes of business.
2) Constraints: restrictions on cost, availability of technical expertise, equipment to be used,
areas of business, which are to be left unchanged and so on.
3) Timescales: when each stage should be completed
4) Reports or outputs required
5) Problems that have been identified with current system
6) Suggested solutions considered by management, these may include possible technical
solutions to the problem, but equally it may also include manual alternatives available.
Why is it important that analyst documents the Terms of Reference before analysis begins ?
The problem definition is more properly defined in the feasibility study.
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The feasibility study
The aim of the feasibility study is to understand the problem and to determine whether it’s worth,
or indeed possible, to computerise the system.
The scope and objectives of the proposed system must be established and documented.
The feasibility study can be broken down into several factors
Technical
Feasibility
Economical
Feasibility
Social
Feasibility
Legal
Feasibility
Operational
Feasibility
Schedule
Feasibility
 Technical Feasibility
Means investigating whether the technology exists to design the proposed system.
Nowadays, as there are so many advances in technology it also involves looking at which
software/hardware which will best meet the proposed objectives. It looks at technical
facilities, such as is there a faculty to produce output in time, for example can 3000
envelopes be produced in one week.
 Economic Feasibility
Is concerned with the cost effectiveness of the proposed system. If the benefits do not
outweigh the cost then it’s not worth developing the system. Other considerations involve
considering the H/W , S/W costs – can they be met within budget. Technical personnel can
be expensive, again their costs need to be taken into account. Also consider: i)
development costs
ii)
running costs
The benefits may be :i)
ii)
Direct economic benefits
Benefits that are hard to quantify e.g. improved management
information or improved customer service – these are know as
Tangible benefits and although are hard to quantify they must
be included in the feasibility report.
 Social Feasibility
This is concerned with the effect on employees and customers on the introduction of a new
system. Will it result in redundancies? Will some jobs be deskilled ? Is there a need for retraining ? Will the workforce be able to cope with the new changes ? Will the workforce have
to relocate ? It is imperative that users are being involved and their cooperation is secured
before changes are made. Equally the effect on customer services have to be identified.
 Legal Feasibility
Determines if there are any legal implications/requirements associated with the introduction
of the new system e.g violation of the Data Protection Act.
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 Operational Feasibility
Is concerned with human, organisational and political aspects. It deals with issues such as,
Whether the current work procedures are adequate enough to support the new system, or
what job changes will the new system bring, what organisational changes will the new system
bring about.
 Schedule Feasibility
Looks at the time it will take to develop the proposed system and whether it will be done with
in the proposed time frame.
On completion of this phase the systems analyst produces a FEASIBILITY REPORT, which
details all the above considerations. The report should state whether it’s feasible to go ahead
with the project or not. This is then agreed and ‘signed off ‘ by senior managers and the
detailed requirements analysis phase begins
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At the end of each phase a ‘deliverable’ is produced.
Phase
Problem definition
DELIVERABLES
- Terms of Reference document
Feasibility Phase
- Feasibility report
- Project plan
- Cost/Benefit Analysis
Analysis Phase
- Detailed Requirements Report
- Revised project plan
- Cost Benefit Analysis
Design Phase
- File Definitions, Program Specifications
-Specifications of operational procedures
-H/W specifications
Construction/
Implementation
- Documented programs
- Test data & Results
- User Manuals
- Working system
Maintenance
- correction of bugs
-Modifications of new requirements
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