Tips for functional analysis

The construction of the FAST diagram may be made easier by using the following tips

  • Start by identifying general functions and then get more specific by asking ‘how?’ – name each function with a verb/noun pair
  • Chronologically trace through each function that must be accomplished – this makes it less likely that key requirements will be missed
  • Include all special modes of operation such as stand-by, run, cleaning – functions that are not part of the normal operation are as important as those that are
  • Avoid specifying form, structure or solutions – the functions should describe behaviour, rather than embodiment
  • Customise the FAST diagram – the more information that can be visualised, the more helpful it is

In addition, the operation of most products and services divides readily into “ready-go-stop” functions.

  • Ready - prepare, set, initialise
  • Go - operate, start, steps of operation
  • Stop - clean up, dispose, save data
The task of taking a picture is broken down into two further levels of sub-functions

A further breakdown of sub-functions into lower-level functions