Experimental Analysis of Numeric and Symbolic ConstraintSatisfaction Techniques for Temporal Reasoning

  • Authors:
  • Malek Mouhoub;Francois Charpillet;Jean Paul Haton

  • Affiliations:
  • LORIA, BP 239, 54506 Vandoeuvre-lès-Nancy, France;LORIA, BP 239, 54506 Vandoeuvre-lès-Nancy, France;LORIA, BP 239, 54506 Vandoeuvre-lès-Nancy, France

  • Venue:
  • Constraints
  • Year:
  • 1998

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Abstract

Many temporal applications like planning and schedulingcan be viewed as special cases of the numeric and symbolic temporalconstraint satisfaction problem. Thus we have developed a temporalmodel, TemPro, based on the interval Algebra, to express suchapplications in term of qualitative and quantitative temporalconstraints. TemPro extends the interval algebra relations ofAllen to handle numeric information. To solve a constraint satisfactionproblem, different approaches have been developed. These approachesgenerally use constraint propagation to simplify the originalproblem and backtracking to directly search for possible solutions.The constraint propagation can also be used during the backtrackingto improve the performance of the search. The objective of thispaper is to assess different policies for finding if a TemPronetwork is consistent. The main question we want to answer hereis ’’how much constraint propagation is useful‘‘ for findinga single solution for a TemPro constraint graph. For this purpose,we have experimented by randomly generating large consistentnetworks for which either arc and/or path consistency algorithms(AC-3, AC-7 and PC-2) were applied. The main result of this studyis an optimal policy combining these algorithms either at thesymbolic (Allen relation propagation) or at the numerical level.