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Counting Solutions to Conjunctive Queries: Structural and Hybrid Tractability
Counting the number of answers to conjunctive queries is a fundamental problem in databases that, under standard assumptions, does not have an efficient solution.
The Computational Complexity of Distinctive Feature Minimization in Phonology
We find that the natural class decision problem is tractable (i. e. is in P), while the minimization problem is not; the decision version of the problem which determines whether a natural class can be defined with $k$ features or less is NP-complete.
Asking the metaquestions in constraint tractability
One formulation of the CSP is as the problem of deciding, given a pair (G, H) of relational structures, whether or not there is a homomorphism from the first structure to the second structure.
An Algebraic Hardness Criterion for Surjective Constraint Satisfaction
The constraint satisfaction problem (CSP) on a relational structure B is to decide, given a set of constraints on variables where the relations come from B, whether or not there is a assignment to the variables satisfying all of the constraints; the surjective CSP is the variant where one decides the existence of a surjective satisfying assignment onto the universe of B.
Beyond Q-Resolution and Prenex Form: A Proof System for Quantified Constraint Satisfaction
We consider the quantified constraint satisfaction problem (QCSP) which is to decide, given a structure and a first-order sentence (not assumed here to be in prenex form) built from conjunction and quantification, whether or not the sentence is true on the structure.
