Quasi-inverses of schema mappings

Schema mappings are high-level specifications that describe the relationship between two database schemas. Two operators on schema mappings, namely the composition operator and the inverse operator, are regarded as especially important. Progress on the study of the inverse operator was not made until very recently, as even finding the exact semantics of this operator turned out to be a fairly delicate task. Furthermore, this notion is rather restrictive, since it is rare that a schema mapping possesses an inverse. In this paper, we introduce and study the notion of a quasi-inverse of a schema mapping. This notion is a principled relaxation of the notion of an inverse of a schema mapping; intuitively, it is obtained from the notion of an inverse by not differentiating between instances that are equivalent for data-exchange purposes. For schema mappings specified by source-to-target tuple-generating dependencies (s-t tgds), we give a necessary and sufficient combinatorial condition for ...

• Type: Conference
• Year: 2007
• Where: PODS
• Authors: Ronald Fagin, Phokion G. Kolaitis, Lucian Popa, Wang Chiew Tan
• Keywords: Database, Inverse Operator, Original Schema Mapping, PODS 2007, Schema Mappings