Why is Requirements Engineering Difficult Software Specification Lecture 2

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Why is Requirements Engineering Difficult?
Software SpecificationLecture 2

• Prepared by
• Stephen M. Thebaut, Ph.D.
• University of Florida

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Fred Brooks, No Silver Bullet... (Info.
Processing, 86)

• The hardest single part of building a software
  system is deciding precisely what to build. No
  other part of the conceptual work is as
  difficult... No other part of the work so
  cripples the resulting system if done wrong. No
  other part is more difficult to rectify later.

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Why is RE so difficult?

• Difficulty of anticipation
• Unknown or conflicting requirements / priorities
• Conflicts between users and procurers
• Fragmented nature of requirements
• Complexity / number of distinct requirements
• Bell (77) missile system with gt8,000 distinct
  requirements and support paragraphs, gt2,500 pages
  of text

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Some analogies

• Working a (dynamically changing!) jigsaw puzzle
• Blind men describing an elephant
• Different specialists describing a patient

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The terminology problem

• problem definition
• problem specification
• requirements (functional or non-functional)
• requirements definition
• requirements specification

• requirements analysis
• systems analysis
• specifications (functional or non-functional)
• software specifications
• systems specification
• design specifications

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Requirement

• ...something required something wanted or
  needed an essential requisite.
• Elicit
• ...to draw forth or bring out to derive by
  reason or argument to evoke.

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Analysis

• ...separation of a whole into its component
  parts an examination of a complex, its elements,
  and their relations resolving complex
  expressions into simpler or more basic ones
  clarification of an expression by an elucidation
  of its use in discourse.
• Specify
• ...to name to state explicitly or in
  (sufficient) detail.

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Why is Requirements Engineering
Difficult?Software SpecificationLecture 2

• Prepared by
• Stephen M. Thebaut, Ph.D.
• University of Florida