Bottom-Up Grounding in the Probabilistic Logic Programming System Fusemate

This paper introduces the Fusemate probabilistic logic programming system. Fusemate's inference engine comprises a grounding component and a variable elimination method for probabilistic inference. Fusemate differs from most other systems by grounding the program in a bottom-up way instead of the common top-down way. While bottom-up grounding is attractive for a number of reasons, e.g., for dynamically creating distributions of varying support sizes, it makes it harder to control the amount of ground clauses generated. We address this problem by interleaving grounding (along program stratification) with a query-guided relevance test. This test prunes ground rules whose heads are inconsistent with the query dynamically extended by the ground rules so far. We present our method in detail and demonstrate it with examples that involve ``time'', such as (hidden) Markov models. Our experiments demonstrate competitive or better performance compared to a state-of-the probabilistic logic programming system, in particular for high branching problems.