Event Calculus Planning Revisited

Murray Shanahan


In 1969 Cordell Green presented his seminal description of planning as theorem proving with the situation calculus. The most pleasing feature of Green's account was the negligible gap between high-level logical specification and practical implementation. This paper attempts to reinstate the ideal of planning via theorem proving in a modern guise. In particular, I will show that if we adopt the event calculus as our logical formalism and employ abductive logic programming as our theorem proving technique, then the computation performed mirrors closely that of a hand-coded partial order planning algorithm. Furthermore, if we extend the event calculus in a natural way to accommodate compound actions, then using exactly the same abductive theorem prover we obtain a hierarchical planner. All this is a striking vindication of Kowalski's slogan "Algorithm = Logic + Control".