Abstract
This chapter addresses the issue of data sharing among autonomous data sources in an environment where constraints cannot be placed on the shared contents of sources. The solutions rely on the use of mapping tables that define how data from different sources are associated. In this setting, the solution to a local query, that is a query posed against the schema of a single source, is augmented by retrieving related data from associated sources. This retrieval of data is achieved by translating, through mapping tables, the local query into a set of queries that are executed against the associated sources. The chapter describes both sound translations (which only retrieve correct answers) and complete translations (which retrieve all correct answers, and no incorrect answers), and presents algorithms to compute such translations.
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