Databases Reference
In-Depth Information
Fig. 9.1
Overview of the matching, mapping, and data exchange tasks
instance. Since mappings are interschema constraints, they may not be enough to
fully specify the target instance. In other words, given a source instance and a set
of mappings between a source and a target schema, there may be multiple target
instances that satisfy the mappings. Finding the best target instance is known in the
literature as the data exchange problem [
Fagin et al. 2005
]. Once the right target
instance is decided, the mappings can be converted into a transformation script that
translates an instance of the source schema into some target schema representation.
This transformation script is typically expressed in some executable language such
as XQuery, XSLT, or SQL.
A mapping tool is a tool that assists the mapping designer in generating the
mappings using less effort, in less time and with fewer mistakes. Mapping tools
can be classified into two large categories based on what they consider as a map-
ping. The first category is the one that makes a clear distinction between mapping
