A Formal Approach to Describing Action Concepts in Taxonomical Knowledge Bases

T his paper outlines a formal theory for de fin ing action concepts in taxonomical knowledge representation languages, in a form closely related to description logics. The central problems of defining an extensional semantics, and, based on this, a subsumption/specialization relation as well as the inheritance of descriptions for action concepts is addressed, as an extension to the respective notions for static object concepts. The suggested approach is based on the view of actions as transformers between world states, where a world state corresponds to an instantiation of object concepts coherent with the knowledge base. A modeltheoretic, extensional semantics for action concepts is defined in accordance with the semantics for object concepts as the set of world states which are in the domain / range of the transformation function associated with the action concept, as specified through the precondition and effect formulae stated in the action description. The specialization/subsumption relation for action concepts is defined based on the set inclusion of the sets of world states which fulfill the precondition (effect) formula.