Qualitative Simulation Based On A Logic Of Space And Time

We describe an envisionment-based simulation program. The program bears some design similarities to Kuipers' QSIM algorithm, but di ers in the underlying ontology and in the implemented theory in the envisioning process. The program implements part of an axiomatic, rst order theory that has been developed to represent and reason about space and time. Topological information is extracted from the modelled domain and is expressed in the theory as sets of distinct topological relations holding betwen sets of objects. These form the qualitative states in the underlying theory and simulation. Processes in the theory are represented in the envisionment as paths in the envisionment tree. We show the feasability of this particular ontology in the implementation of a simulation program derived from a logic-based formal theory. A description of the algorithm is given and the whole is illustrated with an example of a simulation of the processes phagocytosis and exocytosis two processes used by unicellular organisms for garnering food and expelling waste material respectively. Finally we show how the program can be viewed as a specialized theorem prover by mapping program transformations to logical inferences in the modelling theory.