Dealing with Discrepancies in Wrapper Functionality

Much of the world's information is stored electronically in data sources. The data sources can be full-edged databases, simple les, HTML pages or specialized data sources that possess diverse query processing capabilities. The common architecture to integrate such sources consists of mediators that give a global view over the content of all sources, and wrappers that give a local view of each source. Answering queries in this architecture is a diicult problem due to the wide range of capabilities of data sources. This paper presents a solution to this problem in the context of the Disco query processor. We provide a tool to the wrapper implementor to describe the capabilities of the wrapper in ne detail. When a wrapper is registered with the mediator, the mediator uploads the capabilities of the wrapper, and smoothly integrates these capabilities into query processing. Our solution is novel both in the level of detail permitted by the tool and its easy incorporation into existing query optimization strategies. In this paper we describe: the query processing of Disco, the language for specifying wrapper capabilities, the algorithms that integrates these capabilities into query processing, and an implementation of these techniques in the Disco prototype. (a) le traitement de requetes dans Disco, (b) le langage de sp eciication des capacit es des adaptateurs, (c) les algorithmes pour integrer ces capacit es dans le processeur des requ^ etes et (d) l'impl ementation de ces techniques dans notre prototype.