On Reductive Semantics of Aggregates in Answer Set Programming

Several proposals of the semantics of aggregates are based on different extensions of the stable model semantics, which makes it difficult to compare them. In this note, building upon a reductive approach to designing aggregates, we provide reformulations of some existing semantics in terms of propositional formulas, which help us compare the semantics and understand their properties in terms of their propositional formula representations. We also present a generalization of semantics of aggregates without involving grounding, and define loop formulas for programs with aggregates guided by the reductive approach.