Unformatted text preview: satisfaction, including 2-cnfs, Horn clauses, causal networks, and bounded-width networks. Second, we identify new tractable classes based on the notion of diversity . Third, our empirical tests show that, while on uniform theories directional resolution is indeed ineective, on problems with special structures, like chains and k-trees, having low w3 , directional resolution greatly outperforms DP-backtracking which is one of the most eective satisability algorithm known to date. In conclusion, although directional resolution outperformsy DP-backtracking on some classes of problems, it is not advocated as an eective method for general satisability problems. Even when the structure is right, there are other structure-exploiting algorithms, like backjumping, that are likely to be more eective than BDR-DP in nding a satisfying solution. What we do advocate is that structure-based components should be integrated, together with other heuristics (like unit propagation), into any algorithm that tries to solve satisability eectively. At the same time, we have shown that, for some structured domains, directional resolution is an eective knowledge compilation procedure, compiling knowledge into a form that facilitates ecient model generation and query processing. 29 Acknowledgements
We would like to thank Dan Frost, Eddie Schwalb and Rachel Ben-Eliyahu for comments on this paper. Also we would like to thank Dan Frost for running experiments with the backjumping algorithm. 30 References
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- Spring '09
- W. Alabama
- Analysis of algorithms, Conjunctive normal form, Qn, directional resolution