Query Mediation for Heterogeneous Data Sources.
Ulf Leser · 1998
: We present a novel approach to the problem of query mediation in a tight federation of heterogeneous, distributed data sources. It is based on query correspondence assertions (QCAs), which are set-equation between conjunctive queries. We use them as rules to express relationships between heterogeneous and autonomously maintained schemas. We describe an algorithm that uses QCAs to translate queries against the global schema in semantically meaningful and minimal sequences of queries against data sources. A salient feature of our approach is that it is, due to the declarativeness of QCAs, relatively easy to react on schema changes in sources or on the global level. This supports maintainability, which we regard as a key requirement for large-scale projects in information integration. 1. Introduction The recent years have seen a steep increase in the amount of data available for public use, mainly pushed through the success of the World-Wide-Web. For instance, in the field of molecul...