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The Systems Life Cycle: Design

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Designing the new system. The Systems Life Cycle: Design. 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

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Presentation Transcript
so far our analyst has
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
in this next stage the following are designed
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
designing data collection forms screen layouts
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
designing screen layouts
Designing screen layouts
  • Screens must be easy to use
  • Attractive to look at
  • Limit possible errors
  • Guidelines
  • Navigation
  • Input devices
designing report layouts
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)
designing report layouts1
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
designing screen displays
Designing screen displays
  • Keep simple & consistent
  • Not over-elaborate
  • Attractive
  • Navigation
  • Users: no need for advertising
  • Instructions for use
designing data file structures
Designing data & file structures
  • Master files
  • Transaction files
  • Field names
  • Field types
  • Field lengths
  • Validation rules
  • Field descriptions
  • Key field
  • Relationships
  • Test plan
designing validation routines
Designing validation routines
  • As many data validation routines as possible – why?
  • Range checks/length checks/presence checks/format check/
designing other ways of reducing errors
Designing other ways of reducing errors
  • Reducing volume of input data (coding)
  • Direct data entry methods
specifying the required hw sw
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?
software build or buy
Software: Build or Buy?
  • Off the shelf or
  • Purpose built
off the shelf
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
purpose built
Purpose built

Disadvantages:

  • Cost
  • Testing limited to perception of programmer
  • Support limited to team of programmers
  • Time to develop

Advantages:

  • Designed specifically for the task
  • Does not need to be adapted
  • Programmers can make any required changes
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