| Quasi-Stable Semantics of Logic Programs (1998) | |||||||||||||||
Abstract | |||||||||||||||
| this paper, we introduce a new semantic theory for logic programs. We choose the Well-Founded Semantics (WFS) [23] as our starting point because it has many desirable features. For any logic program there exists a unique well-founded partial model which can be defined in a constructive way. WFS naturally extends the semantics for a large class of logic programs, including stratified and locally stratified programs (see [17] and [23]). Despite its merits, it can be argued that the WFS is too "sceptical". For many programs it gives the empty set as their intended meaning. It is thus silent on all atoms though it may be reasonable to expect that something should be concluded from the information given. For an illustrative example, see program P 1 in section 4. There are many proposals for extending the WFS such as the generalised well-founded semantics GWFS [1], the well-founded-by-case-semantics WFSC [20], the extended well-founded semantics WFSE [11], the strong well-founded semantics WFS S [5], and the O-semantics [15]. The relationship between these semantic theories for logic programming is also studied in [6]. Here we propose another nondeterministic extension of the WFS. The other dominant semantic model for logic programs is the stable model semantics [10]. Compared with the WFS, the stable model semantics is "credulous": it derives much more information than the WFS though this is non-deterministic or "disjunctive" in the sense that there may be several stable models for a given logic program. The chief drawback of this semantics is that a stable model is not defined for all logic programs. In addition stable model semantics gives rise to anomalies in some circumstances. See the program P 3 in section 4, borrowed from [23]. A modification of the stable model seman... | |||||||||||||||
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