In Defense of PDDL Axioms

There is controversy as to whether explicit support for PDDL-like axioms and derived predicates is needed for planners to handle real-world domains effectively. Many researchers have deplored the lack of precise semantics for such axioms, while others have argued that it might be best to compile them away. We propose an adequate semantics for PDDL axioms and show that they are an essential feature by proving that it is impossible to compile them away if we restrict the growth of plans and domain descriptions to be polynomial. These results suggest that adding a reasonable implementation to handle axioms inside the planner is beneficial for the performance. Our experiments confirm this suggestion. 1 Motivation It is not uncommon for planners to support derived predicates, whose truth in the current state is inferred from that of some basic predicates via some axioms under the closed world assumption. While basic predicates may appear as effects of actions, derived ones may only be used...

• Type: Conference
• Year: 2003
• Where: IJCAI
• Authors: Sylvie Thiébaux, Jörg Hoffmann, Bernhard Nebel
• Keywords: Basic Predicates, IJCAI 2003, IJCAI 2007, PDDL-like Axioms, Real-world Domains