High Quality Content by WIKIPEDIA articles! The tuple calculus is a calculus that was introduced by Edgar F. Codd as part of the relational model in order to give a declarative database query language for this data model. It formed the inspiration for the database query languages QUEL and SQL of which the latter, although far less faithful to the original relational model and calculus, is now used in almost all relational database management systems as the ad-hoc query language. Lacroix and Pirotte proposed domain calculus, which is closer to first-order logic and showed that these two calculi (and the relational algebra) are equivalent in expressive power. Subsequently query languages for the relational model were called relationally complete if they could express at least all these queries.

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