Constraint Query Languages
A constraint query language is a query language for constraint databases.
The field of constraint databases was initiated in 1990 in a paper by Kanellakis, Kuper, and Revesz . The goal was to obtain a database-style, optimizable version of constraint logic programming. It grew out of the research on datalog and constraint logic programming. The key idea was that the notion of tuple in a relational database could be replaced by a conjunction of constraints from an appropriate language and that many of the features of the relational model could then be extended in an appropriate way. In particular, standard query languages such as those based on first-order logic and datalog could be extended to such a model.
It soon became clear, however, that recursive constraint query languages led to noneffective languages. The focus therefore shifted to non-recursive constraint query languages. The standard query language is the constraint relational calculus (or...
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