We describe an interval logic for reasoning about space. The logic simplifies an earlier theory developed by Randell and Cohn, and that of Clarke upon which the former was based. The theory supports a simpler ontology, has fewer defined functions and relations, yet does not suffer in terms of its useful expressiveness. An axiomatisation of the new theory and a comparison with the two original theories is given.

We describe an envisionment-based simulation program. The program bears some design similarities to Kuipers' QSIM algorithm, but differs in the underlying ontology and in the implemented theory in the envisioning process. The program implements part of an axiomatic, first 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 pro...