Defeasible Specifications in Action Theories
Chitta Baral and Jorge Lobo
Abstract
Recent research in formalizing effects of actions on a world in the
presence of constraints have mostly concentrated on non-defeasible
specifications, where the effect of actions and constraints are
strictly specified. The focus of these research was more on solving
the frame problem (and other problems such as the qualification
and the ramification problem). In this paper we show how to
incorporate defeasibility in the specification and at the same time
solve the frame problem, and the other problems. In our approach
we consider extensions of the high level language `A' of
Gelfond and Lifschitz and introduce defeasible constraints and
effect propositions. While direct semantics of `A' does not
need a logical language, our semantics of the transition
function (i.e., the effect of a single action)
is defined using extended
logic programming. This is due to the defeasibility of the
specification. We then add additional logic programming rules
to the logic programming characterization of the transition function
to reason about the effect of a sequence of actions.