A Hierarchical Situation Calculus

A situation calculus is presented that provides a solution to the frame problem for hierarchical situations, that is, situations that have a modular structure in which parts of the situation behave in a relatively independent manner. This situation calculus is given in a relational, functional, and modal logic form. Each form permits both a single level hierarchy or a multiple level hierarchy, giving six versions of the formalism in all, and a number of sub-versions of these. For multiple level hierarchies, it is possible to give equations between parts of the situation to impose additional structure on the problem. This approach is compared to others in the literature.