MPI-I-93-226
On kernels, defaults and even graphs
Dimopoulos, Yannis and Magirou, Vangelis and Papadimitriou, Christos
June 1993, 11 pages.
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Status: available - back from printing
Extensions in prerequisite-free, disjunction-free default theories have been shown to be in direct correspondence with kernels of directed graphs; hence default theories without odd cycles always have a ``standard'' kind of an extension. We show that, although all ``standard'' extensions can be enumerated explicitly, several other problems remain intractable for such theories: Telling whether a non-standard extension exists, enumerating all extensions, and finding the minimal standard extension. We also present a new graph-theoretic algorithm, based on vertex feedback sets, for enumerating all extensions of a general prerequisite-free, disjunction-free default theory (possibly with odd cycles). The algorithm empirically performs well for quite large theories.
URL to this document: https://domino.mpi-inf.mpg.de/internet/reports.nsf/NumberView/1993-226
BibTeX
@TECHREPORT{Dimopoulos-93-mpii226,
AUTHOR = {Dimopoulos, Yannis and Magirou, Vangelis and Papadimitriou, Christos},
TITLE = {On kernels, defaults and even graphs},
TYPE = {Research Report},
INSTITUTION = {Max-Planck-Institut f{\"u}r Informatik},
ADDRESS = {Im Stadtwald, D-66123 Saarbr{\"u}cken, Germany},
NUMBER = {MPI-I-93-226},
MONTH = {June},
YEAR = {1993},
ISSN = {0946-011X},
}