Closed World Chasing
The authors give a new closed world semantics for data exchange called constructible solutions semantics, and argue that this semantics is well suited for answering non-monotonic queries in data exchange. They show that the space of constructible solutions can be represented by conditional tables obtainable trough a novel conditional chase procedure which generalizes the classical chase. The chase is an algebraic proof procedure originally developed for testing logical implication between (sets of) embedded dependencies. Recently the chase has experienced a revival due to its applications in data exchange. Data exchange consists of transforming a source database into a target database, according to a set of embedded dependencies that describe the mapping between the source and the target database.