The tractability of CSP classes defined by forbidden patterns

  • Authors:

  • David A. Cohen;Martin C. Cooper;Páidí Creed;Dániel Marx;András Z. Salamon

  • Affiliations:

  • Department of Computer Science, Royal Holloway, University of London, Egham, Surrey, UK;IRIT, University of Toulouse III, Toulouse, France;School of Mathematical Sciences, Queen Mary, University of London, Mile End, London, UK;Computer and Automation Research Institute, Hungarian Academy of Sciences, Budapest, Hungary;Laboratory for Foundations of Computer Science, School of Informatics, University of Edinburgh, UK

  • Venue:
  • Journal of Artificial Intelligence Research
  • Year:
  • 2012

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Abstract

The constraint satisfaction problem (CSP) is a general problem central to computer science and artificial intelligence. Although the CSP is NP-hard in general, considerable effort has been spent on identifying tractable subclasses. The main two approaches consider structural properties (restrictions on the hypergraph of constraint scopes) and relational properties (restrictions on the language of constraint relations). Recently, some authors have considered hybrid properties that restrict the constraint hypergraph and the relations simultaneously. Our key contribution is the novel concept of a CSP pattern and classes of problems defined by forbidden patterns (which can be viewed as forbidding generic sub-problems). We describe the theoretical framework which can be used to reason about classes of problems defined by forbidden patterns. We show that this framework generalises certain known hybrid tractable classes. Although we are not close to obtaining a complete characterisation concerning the tractability of general forbidden patterns, we prove a dichotomy in a special case: classes of problems that arise when we can only forbid binary negative patterns (generic subproblems in which only disallowed tuples are specified). In this case we show that all (finite sets of) forbidden patterns define either polynomial-time solvable or NP-complete classes of instances.