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Software Requirements A Use Case Approach

Software Requirements A Use Case Approach. 21 September 2009. Software Requirements. The Rock Problem ?! [Ed Yourdon]. Software systems nature. Software systems by their nature are intangible abstract complex infinitely changeable. Requirements engineering.

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Software Requirements A Use Case Approach

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  1. Software RequirementsA Use Case Approach 21 September 2009

  2. Software Requirements The Rock Problem ?! [Ed Yourdon]

  3. Software systems nature • Software systems by their nature are • intangible • abstract • complex • infinitely changeable

  4. Requirements engineering • Get a complete description of the problem • feasibility study • Get a complete description of the problem • feasibility study • Process of establishing the services that the customer requires from a system • elicitation • specification • validation

  5. Software development • Goal • to develop quality software that meets customers’ needs • What is this software supposed to do? • How, exactly, will we know when the software does exactly that and nothing else?

  6. Software requirement • A software requirement is a capability needed by the user to solve a problem to achieve an objective, and is imposed on the system

  7. Problem domain • The problem domain is the home of those people (real users, other stakeholders) whose needs must be addressed in order to build the perfect system.

  8. problem domain Needs Features solution domain Software requirements

  9. Stage .1-.2 Requirements time Design .5 Coding 1 Unit test 2 5 Acceptance test 20 Maintenance Relative cost to repair a defect Derived from: Alan Davis, Software Requirements: objects,functions and states; Prentice-Hall, 1993

  10. Functional requirements • Find the solution for the user needs by proposing objectives for the system that involves • problem definition • identifying the users • defining the solution system boundary • identifying the constraints

  11. Defining solutions system boundary System Inputs Outputs inputs / system / outputs relationship • Of concern: • Our system • Things that interact with our system actor

  12. System boundary System Boundary I/O Our Solution I/O Users Other Systems

  13. System perspective NewSolution System Boundary Library system Users Catalog system

  14. Use case approach library system Lending services Library user Books database User administration Library staff

  15. Purchase Ticket Traveler Maintenance basic data NS NS Ticket machine – a use case approach Destination Take ticket

  16. Example Use Cases • A simple word processor is required to create new and edit existing documents. • Also the ability to print is required. Question? Find the system boundary, actors and use cases

  17. Study matter • Ian Sommerville Software Engineering , 6th edition – Ch.6 Addison Wesley • Dean Leffingwell & Don Widrig Managing Software Requirements, 2nd edition Addison Wesley

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