DA2 merging operators

A new framework for propositional merging is presented. DA(2) merging operators, parameterized by a distance between interpretations and two aggregation functions, are introduced. Many distances and aggregation functions can be used and many merging operators already defined in the literature (including both model-based ones and syntax-based ones) can be encoded as specific DA(2) operators. Both logical and complexity properties of those operators are studied. An important result is that (under very weak assumptions) query entailment from merged bases is "only" at the first level of the polynomial hierarchy when any of the DA(2) operators is used. As a by-product, complexity results for several existing merging operators are derived as well. (C) 2004 Elsevier B.V. All rights reserved.