Stable and extension class theory for logic programs and default logics

Chitta R. Baral, V. S. Subrahmanian

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


The stable model semantics (cf. Gelfond and Lifschitz [1]) for logic programs suffers from the problem that programs may not always have stable models. Likewise, default theories suffer from the problem that they do not always have extensions. In such cases, both these formalisms for non-monotonic reasoning have an inadequate semantics. In this paper, we propose a novel idea-that of extension classes for default logics, and of stable classes for logic programs. It is shown that the extension class and stable class semantics extend the extension and stable model semantics respectively. This allows us to reason about inconsistent default theories, and about logic programs with inconsistent completions. Our work extends the results of Marek and Truszczynski [2] relating logic programming and default logics.

Original languageEnglish (US)
Pages (from-to)345-366
Number of pages22
JournalJournal of Automated Reasoning
Issue number3
StatePublished - Jun 1992
Externally publishedYes


  • Stable classes
  • default logic
  • extension classes
  • logic programs

ASJC Scopus subject areas

  • Software
  • Computational Theory and Mathematics
  • Artificial Intelligence


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