Uniform CSP Parameterized by Solution Size is in W[1]
share
We show that the uniform Constraint Satisfaction Problem (CSP) parameterized by the size of the solution is in W[1] (the problem is W[1]-hard and it is easy to place it in W[3]). We study the problem on the Boolean domain, that is 0, 1. The size of a solution is the number of variables that are mapped to 1. Named by Kolaitis and Vardi (2000), uniform CSP means that the input contains the domain and the list of tuples of each relation in the instance. Uniform CSP is polynomial time equivalent to homomorphism problem and also to evaluation of conjunctive queries on relational databases. It also has applications in artificial intelligence. We do not restrict the problem to any (finite or infinite) family of relations. Uniform CSP restricted to some finite family of Boolean relations (thus with a bound on the arity of relations) can easily be placed in W[1]. Marx (2005) proved that any such problem is either W[1]-complete or fixed parameter tractable. Together with Bulatov (2014) they extended this result to any finite domain. Our proof gives a nondeterministic RAM program with special properties deciding the problem. First defined by Chen et al. (2005), such programs characterize W[1]. Our work builds upon the work of Cesati (2002), which, answering a longstanding open question, shows that parameterized Exact Weighted CNF is in W[1]. This problem is equivalent to uniform CSP restricted to a specific (infinite) family of Boolean relations, where a tuple is in a relation, if and only if the tuple has exactly one 1. Thus, our result generalizes that of Cesati in at least two ways: There is no bound on the size of the tuples of the relations, and the relations do not need to be symmetric.
READ FULL TEXT
