Query Processing in an Information Mediator

A critical problem in building an information mediator is how to translate a domain-level queries into an efficient query plan for accessing the required data. We have built a flexible and efficient information mediator, called SIMS. SIMS takes a domain-level query and dynamically selects the appropriate information sources based on their content and availability, generates a query access plan that specifies the operations and their order for processing the data, and then performs semantic query reformulation to minimize the overall execution time. This paper describes these three basic components of the query processing in SIMS. 1 Introduction SIMS [ Arens et al., 1993 ] is an information retrieval system that provides an intelligent mediator between information sources and humans users or applications programs. Queries are expressed in a uniform language, independent of the distribution of information over sources, of the various query languages, the location of sources, etc. SIMS d..