From Shapley Value to Model Counting and Back

TL;DR

This paper establishes a polynomial-time equivalence between computing Shapley values and model counting for certain classes of Boolean functions, connecting game-theoretic importance measures with probabilistic query evaluation.

Contribution

It proves a key equivalence linking Shapley value computation to model counting, settling an open problem and enabling new efficient algorithms for specific circuit classes and query types.

Findings

Polynomial-time Shapley value computation for deterministic, decomposable circuits.

Equivalence between Shapley value calculation for query tuples and model counting in lineage.

Hardness results for non-hierarchical Boolean conjunctive queries based on #P-hard model counting.

Abstract

In this paper we investigate the problem of quantifying the contribution of each variable to the satisfying assignments of a Boolean function based on the Shapley value. Our main result is a polynomial-time equivalence between computing Shapley values and model counting for any class of Boolean functions that are closed under substitutions of variables with disjunctions of fresh variables. This result settles an open problem raised in prior work, which sought to connect the Shapley value computation to probabilistic query evaluation. We show two applications of our result. First, the Shapley values can be computed in polynomial time over deterministic and decomposable circuits, since they are closed under OR-substitutions. Second, there is a polynomial-time equivalence between computing the Shapley value for the tuples contributing to the answer of a Boolean conjunctive query and counting the models in the lineage of the query. This equivalence allows us to immediately recover the dichotomy for Shapley value computation in case of self-join-free Boolean conjunctive queries; in particular, the hardness for non-hierarchical queries can now be shown using a simple reduction from the #P-hard problem of model counting for lineage in positive bipartite disjunctive normal form.