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On minimal constraint networks. (English) Zbl 1270.68268

Summary: In a minimal binary constraint network, every tuple of a constraint relation can be extended to a solution. The tractability or intractability of computing a solution to such a minimal network was a long standing open question. Dechter conjectured this computation problem to be NP-hard. We prove this conjecture. We also prove a conjecture by Dechter and Pearl stating that for \(k\geq 2\) it is NP-hard to decide whether a single constraint can be decomposed into an equivalent \(k\)-ary constraint network. We show that this holds even in case of bi-valued constraints where \(k\geq 3\), which proves another conjecture of Dechter and Pearl. Finally, we establish the tractability frontier for this problem with respect to the domain cardinality and the parameter \(k\).

MSC:

68T20 Problem solving in the context of artificial intelligence (heuristics, search strategies, etc.)
68P15 Database theory
68Q17 Computational difficulty of problems (lower bounds, completeness, difficulty of approximation, etc.)

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