Abstract
HEX programs extend logic programs with external computations through external atoms, whose answer sets are the minimal models of the Faber-Leone-Pfeifer-reduct. As already reasoning from Horn programs with nonmonotonic external atoms of polynomial complexity is on the second level of the polynomial hierarchy, answer set checking needs special attention; simply computing reducts and searching for smaller models does not scale well. We thus extend an approach based on unfounded sets to HEX and integrate it in a Conflict Driven Clause Learning framework for HEX program evaluation. It reduces the check to a search for unfounded sets, which is more efficiently implemented as a SAT problem. We give a basic encoding for HEX and show optimizations by additional clauses. Experiments show that the new approach significantly decreases runtime.
This research has been supported by the Austrian Science Fund (FWF) project P20840, P20841, P24090, and by the Vienna Science and Technology Fund (WWTF) project ICT08-020.
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Eiter, T., Fink, M., Krennwallner, T., Redl, C., Schüller, P. (2012). Exploiting Unfounded Sets for HEX-Program Evaluation. In: del Cerro, L.F., Herzig, A., Mengin, J. (eds) Logics in Artificial Intelligence. JELIA 2012. Lecture Notes in Computer Science(), vol 7519. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-33353-8_13
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DOI: https://doi.org/10.1007/978-3-642-33353-8_13
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