Capabilities-Based Query Rewriting in Mediator Systems

Abstract

Users today are struggling to integrate a broad range of information sources that provide different levels of query capabilities. Currently, data sources with different and limited capabilities are accessed either by writing rich functional wrappers for the more primitive sources, or by dealing with all sources at a "lowest common denominator". This paper explores a third approach, in which a mediator ensures that sources receive queries they can handle, while still taking advantage of all the query power of the source. We propose an architecture that enables this, and identify a key component of that architecture, the Capabilities-Based Rewriter We provide a language to describe the query capability of data sources. The CBR takes as input a description of each data sources' capability. Given a query posed to the mediator, the CBR determines the component queries to be sent to the sources, commensurate with their It also computes a plan for combining the results of the component queries using joins, unions, selections, and projections. Our description language and plan generation algorithm are schema independent and handle SPJ queries.