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We study conjunctive queries with unequalities (x ≠ y) and we identify cases when query containment can still be characterized by the existence of homomorphisms. We also identify a class of GLAV-like database schema mappings with unequalities, for which the chase theorem holds, and thus data exchange has the same complexity as for GLAV mappings. Finally, we define a notion of consistency and provide an algorithm to check whether a set of mappings is consistent.
Grigoris Karvounarakis and Val Tannen, "Conjunctive Queries and Mappings With Unequalities", . January 2008.
Date Posted: 22 June 2009