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II. Capturing requirements

A. Types of requirements

  1. Functional requirements

    These describe necessary behaviors of the system such as services provided to users and relationships between these services.

    Examples:
    • "A customer is allowed to select a CD from among all of the CDs in a particular music category, and then may select a song on this CD."
    • "A customer may make multiple selections after inserting sufficient payment (to some limit)."
    • "At any point, a customer may cancel the selection process and if desired have any credited money returned."
    • "Musical selections should be played in the order in which they were made."

  2. Non-functional requirements

    These describe constraints of the system such as response times, computational accuracy, software portability, scalability, maintainability, ... *ility, ....

    Examples:
    • "After making a selection, and assuming no selections are currently playing or pending, the jukebox will start playing the selection within five seconds."
    • "The jukebox design will be scalable to allow the possibility of a future version to hold many more CDs." (Should be more specific.)
    • "Some mechanism will be provided for transfering CD information back and forth between the jukebox and a personal computer. PC software will also be provided for maintaining this data."

  3. Pseudo-requirements

    These restrict how the system will be implemented and supported by existing software products, and how hardware considerations will affect its deployment.

    Examples:
    • "The jukebox software system will be implemented using Java 2."
    • "The jukebox software system will run on top of an embedded Xinu operation system."
    • "The jukebox hardware will be based on a MIPS CPU."


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