Systems Life Cycle

lumpysteerΛογισμικό & κατασκευή λογ/κού

2 Δεκ 2013 (πριν από 3 χρόνια και 10 μήνες)

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Systems Life Cycle


1.Project

Idenification

2. Initial

Investigation

3. Feasibilty

Study

4. Analysis

5. Design

6. Development

and testing

7. Implementation

8. Monitoring

and evalation

Project Identification

This is where an area within an organisation that
has problems processing data is identified


This can be through:



informal discussion



identifying formal terms of reference for


someone else to use


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Initial Investigation

The current system is investigated to find out how the data is
currently processed.


This can be done by:



Questionnaires



Observation



Interviews

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Feasibility Study

At this stage a decision is made as to whether it is
sensible (feasible) to design a new system or whether the
existing system is adequate.


A Feasibility Report is written which includes:


cost/benefit analysis


preliminary analysis and design of a new system



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Analysis

A full analysis is now carried out based on a detailed
investigation of the current system and what the new system
is required to do.


The results of the investigation are documented ( written
down) and a Requirements Specification is written


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Design

A design specification is written which meets all the items in
the requirement specification.


The design specification includes:



inputs



outputs



data structures


data processing required



security measures

recovery procedures




software


hardware


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Development and Testing

At this stage the following is carried out:


data structures are set up


a test strategy is decided on
-

using normal, unusual


and extreme data


results of testing are documented and action taken if

the tests do not work


user documentation is written,tested and amended as

necessary

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Implementation

At this stage the new system is introduced and staff trained.

This is done in one of the following ways:


Direct Changeover



Phased Changeover



Parallel Running



Pilot Running


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Monitoring and Evaluation

One the system has been implemented it is still monitored and
its performance is evaluated.


The system is modified as necessary when the requirements for
data processing change.

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Questionnaires

Advanatges


efficient method of
collecting data


saves time as people
are not taken away
from their jobs to
discuss issues


makes people focus
on the issues in the
questionnaire


Disadvantages

Sometimes people do not
return them

people may not understand
the questions

may be time consuming to
complete

some issues may not be
included


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Observation

Advantages


a clear picture of the
processes involved is
obtained

Disadvanatges

the person observed
may resent it


people may change their
behaviour while being
observed

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Interviews

Advantages


It is possible to discuss some
facts in more detail

Disadvanatges


They take a long time to carry
out

It may be difficult to find a
time during the working day
to do the interview

It can be difficult to keep
focussed on the important
issues


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Direct Changeover

The changeover form the old system to the new one takes
place completely overnight


Staff have to use the new system immediately


If the system fails there is no other system to return to

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Phased Changeover

Parts of the system are implemented a little at a time


Users have the chance to get used to the changes in the
system gradually


Any errors that are found in the new system can be fixed
in a more manageable way

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Parallel Running

Both the old and the new systems are run together for a
time


This means that all the data must be processed twice while
both systems are being used


Any errors in the new system will not affect the normal
output while the old system is working

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Pilot Running

The new system is run on a trial basis with only a small
number of users using it.


This allows any errors to be identified and corrected with
very little effect on normal processing and output

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