Establishing an XML metadata klnowledge base to assist integration of structured and semi-structured databases

This paper describes the establishment of an XML Metadata Knowledge Base (XMKB) to assist integration of distributed heterogeneous structured data residing in relational databases and semi-structured data held in wellformed XML documents (XML documents that conform to the XML syntax rules but have no referenced DTD or XML schema) produced by internet applications. We propose an approach to combine and query the data sources through a mediation layer. Such a layer is intended to establish and evolve an XMKB incrementally to assist the Query Processor to mediate between user queries posed over the master view and the distributed heterogeneous data sources. The XMKB is built in bottom-up fashion by extracting and merging incrementally the metadata of the data sources. The XMKB is introduced to maintain the data source information (names, types and locations), metainformation about relationships of paths among data sources, and function names for handling semantic and structural discrepancies. A System to Integrate Structured and Semi-structured Databases (SISSD) has been built that generates a tool for a meta-user (who does the metadata integration) to describe mappings between the master view and local data sources by assigning index numbers and specifying conversion function names. This system is flexible: users can get any master view from the same set of data sources depending on their interest. It also preserves local autonomy of the local data sources. The SISSD uses the local-as-view approach to map between the master view and the local schema structures. This approach is well-suited to supporting a dynamic environment, where data sources can be added to or removed from the system without the need to restructure the master view and to regenerate the XMKB from scratch.