Design of Query Reformulation Engine in Data Access and Integration System

This paper introduces three core modules of query reformulation engine, mapping document, query reformulation module, and statement conversion module. Mapping document is an XML document that keeps the mapping information between local data source and related data sources; using mapping document, applications could find data sources that have mapping relationship with its local data source. The query reformulation module reformulates the query statements submitted by users to local data resource to query statements to all data sources that have mapping relationship with local data resource. The statement conversion module converts XPath statements to OQL statements that are supported by OGSA-DQP; through OGSA-EDAI in the bottom layer, the access result to the data sources could be obtained. When a user submits an XPath statement to OGSA-DQP, it calls the query reformulation module, which first checks the mapping document to find information of other data sources, then expands and reformulates this XPath statement into query statements that are suitable for the mapped data sources. Afterward, the statement conversion module converts the reformulated XPath statements into OQL statements and returns to OGSA-DQP, which then performs the query operation.