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The Systems Life Cycle: Design

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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The Systems Life Cycle: Design

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

  2. 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

  3. 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

  4. 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

  5. Designing screen layouts • Screens must be easy to use • Attractive to look at • Limit possible errors • Guidelines • Navigation • Input devices

  6. 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)

  7. 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

  8. Designing screen displays • Keep simple & consistent • Not over-elaborate • Attractive • Navigation • Users: no need for advertising • Instructions for use

  9. Designing data & file structures • Master files • Transaction files • Field names • Field types • Field lengths • Validation rules • Field descriptions • Key field • Relationships • Test plan

  10. Designing validation routines • As many data validation routines as possible – why? • Range checks/length checks/presence checks/format check/

  11. Designing other ways of reducing errors • Reducing volume of input data (coding) • Direct data entry methods

  12. 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?

  13. Software: Build or Buy? • Off the shelf or • Purpose built

  14. 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

  15. 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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