Metadata refers to data about the meaning, content, organization, or purpose of data. Metadata may be as simple as a relational schema or as complicated as class library or information describing the derivation, accurancy, and history of individual data items.
In [10], Sciore, Siegel and Rosenthal describe a metadata approach to facilitate interoperability among heterogeneous information systems. Their approach uses semantic values in the context of relational model and provide transparent context conversions and manipulations of metadata and a context mediator to capture the context-related meta information. In [8], McCarthy presents a metadata representation language. It allows the inclusion of a wide range of metadata accessible through a set of operators specially defined for metadata manipulation. [3] uses knowledge-based representation for metadata. However, neither of these methods discuss the practical means for defining comparable concepts and relating concepts at schema level and data level to facilitate the processing of queries over heterogeneous data sources.
We intend to use metadata to address the following questions: