What is Functional requirements

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  • Describe functionality or system services.
  • Depend on the type of software, expected users and the type of system where the software is used.
  • Functional user requirements may be high-level statements of what the system should do.
  • Functional system requirements should describe the system services in detail.

Examples: Functional requirements for the MHC-PMS

  • A user shall be able to search the appointments lists for all clinics.
  • The system shall generate each day, for each clinic, a list of patients who are expected to attend appointments that day.
  • Each staff member using the system shall be uniquely identified by his or her 8-digit employee number.

Requirements imprecision

  • Problems arise when requirements are not precisely stated.
  • Ambiguous requirements may be interpreted in different ways by developers and users.
  • Consider the term ‘search’ in requirement 1
    • User intention – search for a patient name across all appointments in all clinics;
    • Developer interpretation – search for a patient name in an individual clinic. User chooses clinic then search.

Requirements completeness and consistency

  • In principle, requirements should be both complete and consistent.
    • Complete-They should include descriptions of all facilities required.
    • Consistent-There should be no conflicts or contradictions in the descriptions of the system facilities.
  • In practice, it is impossible to produce a complete and consistent requirements document.

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