Temporal aspects of functional modelling for design analysis

Qualitative simulation interpreted by the use of functional labels to identify significant system behaviour has been shown to be a useful technique for automating design analysis tasks such a Failure Modes and Effects Analysis. However, increasing sophistication of the systems to be analysed means that it is becoming increasingly important that the correct timing of these system functions be included in the analysis but the existing functional labels do not capture this information. This paper discusses difficulties arising from this lack and the problems of modelling timing of achievement of functions. It proposes a simple approach to modelling temporal aspects of system function that allows both non achievement and unexpected achievement of a system function to be detected in design analysis as well as showing situations when a function is achieved later (or earlier) than it should be.