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Usability > Assessment Tools - 2 of 7

Task Analysis Tools Used Throughout Development

There are many task analysis tools available to support human-centered design.  These tools are used to define, evaluate, and document function and task flows throughout development.  They are iteratively addressed and refined, providing a visual, graphic representation that is used to focus discussion and decisions on system design.  The task analysis tools that will be addressed in this section are:  Functional Flow Diagrams, Flow Process Charts (FPC), Decision/Action Diagrams, Operational Sequence Diagrams (OSDs), and Human Error Analyses (HEA).

  • Functional Flow Diagrams - Also referred to as functional block diagrams, functional flows, and functional flow block diagrams, these diagrams graphically depict system functions and the sequence and interrelationships of these functions.  Initial diagrams are high level and do not include function allocation.  As design efforts progress, levels of detail are added such as function allocation, data/information interchange, frequency, and timing. Arrows indicate the normal sequence of functions.  Reference block numbering indicates the function level and association for traceability as functions are decomposed.  Points at which arrows join or split are connected by "and," "or," or "and/or" junctions or gates.

Below is a graphical explanation of a function "block" used in these diagrams.  Flow is from left to right.  Functional flow diagrams are decomposed into multiple levels of finer detail.  On the next page, three-levels of a functional flow diagram are presented for illustrative purposes.

Functional Flow Diagrams



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