Adaptive CHR Meets CHRv: An Extended Refined Operational Semantics for CHRv Based on Justifications

Adaptive constraint processing with Constraint Handling Rules (CHR) allows the application of intelligent search strategies to solve Constraint Satisfaction Problems (CSP), but these search algorithms have to be implemented in the host language of adaptive CHR, which is currently Java. On the other hand, CHR enables to explicitly formulate search in CHR, using disjunctive bodies to model choices. However, a naive implementation for handling disjunctions, in particular chronological backtracking (as implemented in Prolog) might cause “thrashing” due to an inappropriate order of decisions. To avoid this, a first combination of adaptive CHR and CHR is presented to offer a more efficient embedded search mechanism to handle disjunctions. Therefore the refined operational semantics of CHR is extended for disjunctions and adaptation.