Scaling Heterogeneous Databases and the Design of Disco

: Access to large numbers of data sources introduces new problems for users of heterogeneous distributed databases. End users and application programmers must deal with unavailable data sources. Database administrators must deal with incorporating each new data source into the system. Database implementors must deal with the transformation of queries between query languages and schemas. The Distributed Information Search COmponent (DISCO) addresses these problems. Query processing semantics give meaning to queries that reference unavailable data sources. Data modeling techniques manage connections to data sources. The component interface to data sources flexibly handles different query languages and different interface functionalities. This paper describes in detail (a) the distributed mediator architecture of DISCO, (b) its query processing semantics, (c) the data model and its modeling of data source connections, and (d) the interface to underlying data sources. We describe several ..