From domain-landmark graph learning to problem-landmark graph generation

Abstract: Landmarks have long played a pivotal role in automated planning, serving as crucial elements for improving the planning algorithms. The main limitation of classical landmark extraction methods is their sensitivity to specific planning tasks. This results in landmarks fully tailored to individual instances, thereby limiting their applicability across other instances of the same planning domain. We propose a novel approach that learns landmark relationships from multiple planning tasks of a planning domain. This leads to the creation of a \textit{probabilistic lifted ordering graph}, as a structure that captures weighted abstractions of relationships between parameterized landmarks. Although these orderings are not 100\% true (they are probabilistic), they can still be very useful in planning. Next, given a new planning task for that domain, we instantiate the relationships from that graph to this particular instance. This instantiation operates in two phases. First, it generates two graphs: the former instantiating information from the initial state and the latter from the goal state. Second, it combines these two graphs into one unified graph by searching equivalences to extract landmark orderings. We evaluate the precision and recallof the information found by our approach over well-known planning domains.