Usability Engineering

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Usability Engineering
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Usability Engineering

• Usability specifications
• quantify the usability of a system - no
  universal definition of the term
• specifications take the form of precise
  statements of performance goals.
• Typically related to
• Ease of learning (Learnability)
• Efficiency (Throughput)
• Subjective matters of user satisfaction

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Usability specifications

• Important because they offer a way of
  incorporating usability into software quality
  assurance specifications
• Example (of a data retrieval system)
• 90 of all users will be able to identify the
  location of a book in the library by its shelf
  number, given the authors name and book title,
  within ten seconds...

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Objective of usability specifications

• To make decisions about user interface goals
  explicit
• Support effective collaboration within the design
  team, between its members

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Components of a usability specification

• Statement of the usability attribute
• Statement of the criteria which will represent
  attainment of the specification
• Now level
• Worst case
• Planned level
• Best case
• Statement of which set or subset of users the
  specification applies to
• A statement of preconditions for the measurement

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Sample specification

• For an UNDO operation on a VCR
• Attribute Backward recoverability (measuring
  concept of undoing an erroneous programming
  sequence)
• Measuring method Number of explicit user actions
  needed to complete an UNDO
• Now level No current product allows such an undo
• Worst case As many actions as it takes to
  program the error
• Planned level A maximum of two explicit user
  actions
• Best case One explicit cancel action
• User class All
• Preconditions Programming error has not
  crashed the VCR, or caused abnormal failure