| Of the numerous formal approaches that deal with database inconsistencies with respect to integrity constraints, all share the view that such constraints are statements about the world the database models. An alternative perspective, however, considers constraints as statements about the knowledge the database has of its domain. The result of this shift in perspective allows us to regard integrity constraint violations as a fragment of the incomplete knowledge the system has of the world. We can then query the possibly inconsistent database for consistent query answers.;We address the above considerations with an epistemic query language KL where the possible ways to repair a database that violates its integrity constraints are characterized by a set of possible worlds, an epistemic state eC. This culminates in a situation where only consistent information is known. We ascertain this by querying eC with KL , providing a knowledge-level formalization of consistent query answers. At the outset, we show that KL is an adequate language for querying databases by specifying a class of admissible formulas for which the set of answers to such queries are safe and domain independent. After formulating database dependencies in KL , we prove that they are members of this class. A Prolog-like sound and complete query evaluator, cqa, for admissible KL formulas is presented. Finally, we completely characterize what is known in eC with a set of first-order sentences. |
