A denotational semantics for equilibrium logic*. Issue 4 (3rd September 2015)

• Record Type: Journal Article
• Authors: AGUADO, FELICIDAD; CABALAR, PEDRO; PEARCE, DAVID; PÉREZ, GILBERTO; VIDAL, CONCEPCIÓN
• Editors: Eiter, Thomas; Toni, Francesca
• Is Part Of: Theory and practice of logic programming. Volume 15:Issue 4/5(2015)
• Page Start: 620
• Page End: 634
• Publication Date: 2015-09-03
• Subjects: Answer Set Programming, -- Equilibrium Logic; Logic programming -- Periodicals; Artificial intelligence -- Computer programs -- Periodicals; Constraint programming (Computer science) -- Periodicals; 005.115
• DOI: 10.1017/S1471068415000277
• Languages: English
• ISSNs: 1471-0684

Abstract

Abstract: In this paper we provide an alternative semantics for Equilibrium Logic and its monotonic basis, the logic of Here-and-There (also known as Gödel's G 3 logic) that relies on the idea of denotation of a formula, that is, a function that collects the set of models of that formula. Using the three-valued logic G 3 as a starting point and an ordering relation (for which equilibrium/stable models are minimal elements) we provide several elementary operations for sets of interpretations. By analysing structural properties of the denotation of formulas, we show some expressiveness results for G 3 such as, for instance, that conjunction is not expressible in terms of the other connectives. Moreover, the denotational semantics allows us to capture the set of equilibrium models of a formula with a simple and compact set expression. We also use this semantics to provide several formal definitions for entailment relations that are usual in the literature, and further introduce a new one called strong entailment . We say that α strongly entails β when the equilibrium models of α ∧ γ are also equilibrium models of β ∧ γ for any context γ. We also provide a characterisation of strong entailment in terms of the denotational semantics, and give an example of a sufficient condition that can be applied in some cases.