Technical Reports (CIS)
Document Type
Technical Report
Date of this Version
January 2008
Abstract
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.
COinS
Date Posted: 22 June 2009
Comments
University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-08-37