![]() We also consider local-as-view mediation, which requires effort even to figure out how to compose the answer to a query from defined views, but which offers advantages in flexibility of operation. We examine capability-based optim ization for gl obal- as-vie w mediators. Med iator systems can be divided i nto two c las ses: “ global- as-view” (the da ta a t th e inte grate d data bas e is defi ned b y how it is constructed from the sources) and “local-as-view” (the content of the sour ces i s def ine d in terms of the schema tha t the integrated d atabase supports). Information-integration systems require special kinds of query-optimization techniques for the ir eff ic ien t operation. ![]() The solution lie s in the desi gn of “ wrappers” - transla tors betwee n the schema and d ata val ue s at a source and the schema and data values at the integrated database. We begin by exploring the ways in which seemingly similar databases can actua lly embody confl icts th a t a re hard to resol ve correc tly. The sources may be con ventional databases or other types of information, such as collections of Web pages. The integrated databa se may be p hysic al (a “warehouse”) or virtual (a “mediator” or “middleware” that may be queried even thoug h its does not exist physical ly). ![]() ![]() Is the process of taking several databases or other in formation sources and making the data in these sources work together as if they were a s ing le database. ![]()
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