In this paper, we initiate a systematic study of the parametrised complexity in the field of Dependence Logics which finds its origin in the Dependence Logic of Väänänen from 2007. We study a propositional variant of this logic (PDL) and investigate a variety of parametrisations with respect to the central decision problems. The model checking problem (MC) of PDL is NP-complete. The subject of this research is to identify a list of parametrisations (formula-size, treewidth, treedepth, team-size, number of variables) under which MC becomes fixed-parameter tractable. Furthermore, we show that the number of disjunctions or the arity of dependence atoms (dep-arity) as a parameter both yield a paraNP-completeness result. Then, we consider the satisfiability problem (SAT) showing a different picture: under team-size, or dep-arity SAT is paraNP-complete whereas under all other mentioned parameters the problem is in FPT. Finally, we introduce a variant of the satisfiability problem, asking for teams of a given size, and show for this problem an almost complete picture.
ACM Subject Classification Theory of computation → Complexity theory and logic; Theory of computation → Parameterized complexity and exact algorithmsContributions In Table 1, we give an overview of our results. We study eight different parametrisations for each of the model checking problem, the satisfiability problem, as well as a variant of satisfiability (this problem asks for a team of a given size). Thereby, we prove dichotomies for MC and SAT: depending on the parameter the problem is either fixed-parameter tractable or paraNP-complete. Only the satisfiability variant and the parameters treewidth and dep-arity resist a complete classification and are left for further research.
Related workThe technique of Courcelle's theorem [4] (see Prop. 6) has been used in different contexts: temporal logic [23], knowledge representation [13], and nonmonotonic logic [25]. Elberfeld et al. [10] enriched Courcelle's theorem to also yield results for the complexity class XL. This improvement applies to our results utilising this theorem as well and affects Theorem 12, 16, and 25.Organisation of the article At first, we introduce some required notions and definitions in (parametrised) complexity theory, dependence logic, and first-order logic. Then we study the parametrised complexity of the model checking problem. Proceed with the satisfiability problem and study a variant of it. Finally, we conclude and discuss open questions. Proofs of results marked with a ( ) can be found in the appendix.