DA2 merging operators Original Research Article

A new framework for propositional merging is presented. DA2 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 DA2 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 DA2 operators is used. As a by-product, complexity results for several existing merging operators are derived as well.