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Recently, attention has been focussed on historical databases (HDBs), representing an enterprise over time. We have developed a new language, TQuel, to query an HDB. TQuel is a superset of Quel, the query language in the Ingres relational database management system. This paper provides an overview of the language, motivating the various design decisions with the objective that it be a minimal extension, both syntactically and semantically, of Quel.
Richard T. Snodgrass (Sun,) studied this question.