We present in this paper a new framework for propositional merging. Distance-based 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 recovered as specific distance-based operators. Both logical and complexity properties of distance-based merging 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 our distance-based operators is used. As a by-product, complexity results for several existing merging operators are derived as well.
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