Inverting schema mappings

A schema mapping is a specification that describes how data structured under one schema (the source schema) is to be transformed into data structured under a different schema (the target schema). Although the notion of an inverse of a schema mapping is important, the exact definition of an inverse mapping is somewhat elusive. This is because a schema mapping may associate many target instances with each source instance, and many source instances with each target instance. Based on the notion that the composition of a mapping and its inverse is the identity, we give a formal definition for what it means for a schema mapping M to be an inverse of a schema mapping M for a class S of source instances. We call such an inverse an S-inverse. A particular case of interest arises when S is the class of all instances, in which case an S-inverse is a global inverse. We focus on the important and practical case of schema mappings defined by source-to-target tuple-generating dependencies, and unco...

• Type: Conference
• Year: 2006
• Where: PODS
• Authors: Ronald Fagin
• Keywords: Database, Inverse Mapping, PODS 2006, Schema Mapping, Target Schema