Conjunctive Queries and Mappings With ... - ScholarlyCommons
University of Pennsylvania
ScholarlyCommons Technical Reports (CIS)
Department of Computer & Information Science
January 2008
Conjunctive Queries and Mappings With Unequalities Grigoris Karvounarakis University of Pennsylvania
Val Tannen University of Pennsylvania, [email protected]
Follow this and additional works at: http://repository.upenn.edu/cis_reports Recommended Citation Grigoris Karvounarakis and Val Tannen, "Conjunctive Queries and Mappings With Unequalities", . January 2008.
University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-08-37 This paper is posted at ScholarlyCommons. http://repository.upenn.edu/cis_reports/906 For more information, please contact [email protected].
Conjunctive Queries and Mappings With Unequalities 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. Comments
University of Pennsylvania Department of Computer and Information Science Technical Report No. MSCIS-08-37
This technical report is available at ScholarlyCommons: http://repository.upenn.edu/cis_reports/906
Conjunctive queries and mappings with unequalities Grigoris Karvounarakis
Val Tannen
Computer and Information Science Department University of Pennsylvania
{gkarvoun,val}@cis.upenn.edu Abstract We study conjunctive queries with unequalities (x 6= 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.
1
Introduction
Containment of queries in general or under dependencies is an important problem that has been studied extensively in database research. Statements of conjunctive query containment are themselves related to very general database dependencies and to schema mappings (GLAV). The applications include query optimization, data integration, and data exchange. The chase procedure gives an algorithm for testing containment of conjunctive queries under certain classes of depedencies [10, 11]. Moreover, for GLAV schema mappings the chase can also be used to solve the problem of data exchange [11]. The results we just mentioned assume conjunctions of positive atoms in the queries, dependencies and mappings and the corresponding algorithms have reasonable complexity (for fixed schemas). However, it is known that the introduction of negation or inequalities (i.e.,
ScholarlyCommons Technical Reports (CIS)
Department of Computer & Information Science
January 2008
Conjunctive Queries and Mappings With Unequalities Grigoris Karvounarakis University of Pennsylvania
Val Tannen University of Pennsylvania, [email protected]
Follow this and additional works at: http://repository.upenn.edu/cis_reports Recommended Citation Grigoris Karvounarakis and Val Tannen, "Conjunctive Queries and Mappings With Unequalities", . January 2008.
University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-08-37 This paper is posted at ScholarlyCommons. http://repository.upenn.edu/cis_reports/906 For more information, please contact [email protected].
Conjunctive Queries and Mappings With Unequalities 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. Comments
University of Pennsylvania Department of Computer and Information Science Technical Report No. MSCIS-08-37
This technical report is available at ScholarlyCommons: http://repository.upenn.edu/cis_reports/906
Conjunctive queries and mappings with unequalities Grigoris Karvounarakis
Val Tannen
Computer and Information Science Department University of Pennsylvania
{gkarvoun,val}@cis.upenn.edu Abstract We study conjunctive queries with unequalities (x 6= 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.
1
Introduction
Containment of queries in general or under dependencies is an important problem that has been studied extensively in database research. Statements of conjunctive query containment are themselves related to very general database dependencies and to schema mappings (GLAV). The applications include query optimization, data integration, and data exchange. The chase procedure gives an algorithm for testing containment of conjunctive queries under certain classes of depedencies [10, 11]. Moreover, for GLAV schema mappings the chase can also be used to solve the problem of data exchange [11]. The results we just mentioned assume conjunctions of positive atoms in the queries, dependencies and mappings and the corresponding algorithms have reasonable complexity (for fixed schemas). However, it is known that the introduction of negation or inequalities (i.e.,
