The Systems Life Cycle: Design
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Transcript of The Systems Life Cycle: Design
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The Systems Life Cycle: Design
Designing the new system
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So far, our analyst has….
Collected information on how the current system works
Established inputs, processes & outputs
Recorded information Identified problems Identified suitable hardware
& software Identified user & information
requirements
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In this next stage, the following are designed: Inputs to the system Outputs from the system Files/databases needed to store the
data The processing required to produce
the outputs Any validation required The data needed to test the system
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Designing data collection forms/screen layouts
DCFs can be paper based or on screen
Need to take great care – why? Easy for workers to fill Easy for secretary to read Eg one box per character Minimise errors Requirements must be clear Design may depend on user
requirements/required output
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Designing screen layouts
Screens must be easy to use
Attractive to look at Limit possible errors Guidelines Navigation Input devices
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Designing report layouts Influenced by views of user Also by user requirements Attractive Not over-elaborate Instructions for navigation Output format
(graphs/lists/reports/tables)
Medium (paper/screen/sound)
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Designing report layouts Layout: who sees it? –
users and customers, so need to consult with Company
Easy to read Professional Style: house style 3 or 4 different designs
for approval
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Designing screen displays Keep simple &
consistent Not over-elaborate Attractive Navigation Users: no need for
advertising Instructions for use
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Designing data & file structures Master files Transaction files Field names Field types Field lengths Validation rules Field descriptions Key field Relationships Test plan
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Designing validation routines As many data
validation routines as possible – why?
Range checks/length checks/presence checks/format check/
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Designing other ways of reducing errors Reducing volume
of input data (coding)
Direct data entry methods
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Specifying the required HW & SW Final stage Earlier: general
recommendations Now: specific
May include supplier details
Volume of data may determine input/output devices
Storage: indexed sequential or sequential?
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Software: Build or Buy?
Off the shelf or Purpose built
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Off the shelf
Advantages: Mass produced so
cheaper Available straight
away Rigorously tested Helplines etc
available
Disadvantages: Cannot be
adapted/difficult to adapt
May have distracting extra features (eg Office Paperclip)
May not match existing system & software
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Purpose built
Advantages: Designed
specifically for the task
Does not need to be adapted
Programmers can make any required changes
Disadvantages: Cost Testing limited
to perception of programmer
Support limited to team of programmers
Time to develop