| Summary: | Ticker-2 is a Qualitative Model of cardiac electrophysiology. One of the motivations was a desire to test and improve Qualitative Modelling techniques by their application to a real-world problem. The approach used is component-based, but, unlike much other work in Qualitative Modelling, discrete valued parameters are used. The application of temporal constraints play an important part, and the Relative Endpoint Duration formalism has been developed to constrain the generation of behaviours by the application of knowledge about the domain. This formalism is unusual in Qualitative Modelling in that an explicit 'unknown' value is used, instead of allowing uncertain values to lead to nondeterministic branching. Both simulation and envisionment have been used to generate behaviours from Ticker-2. Problems exist with both, but envisionment being more appropriate to the domain of cardiac electrophysiology, a number of ways of overcoming difficulties with envisionment are developed. An approach to comparing the behaviours of Ticker-2 with KARDIO behaviours is also suggested.
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