Introduction to the special issue on programming with answer sets

The search for an appropriate characterization of negation as failure in logic programs in the mid 1980s led to several proposals. Amongst them the stable model semantics – later referred to as answer set semantics, and the well-founded semantics are the most popular and widely referred ones. According to the latest (September 2002) list of most cited source documents in the CiteSeer database (http://citeseer.nj.nec.com) the original stable model semantics paper (Gelfond and Lifschitz, 1988) is ranked 10th with 649 citations and the well-founded semantics paper (Van Gelder et al., 1991) is ranked 70th with 306 citations. Since 1988 – when stable models semantics was proposed – there has been a large body of work centered around logic programs with answer set semantics covering topics such as: systematic program development, systematic program analysis, knowledge representation, declarative problem solving, answer set computing algorithms, complexity and expressiveness, answer set computing systems, relation with other non-monotonic and knowledge representation formalisms, and applications to various tasks