Schema versioning: queries to the generalized temporal database system

Raw data and database structures are evolving entities that require adequate support for past, present and even future versions. Temporal databases supporting schema versioning were developed with the aim of satisfying this requirement. This paper considers a generalized temporal database system, which provides support for time at both intensional and extensional levels. The support for schema versioning raises two complex subjects: the storage of the several schema versions and their associate data, and the processing of queries involving more than one schema version. The main goal of this paper is to analyse the second aspect in order to propose a strategy to answer multi-schema queries.