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Imielinski
We now describe the notion of a query more formally. Traditionally,
queries in databases are expressed using two different formalisms: the rela-
tional algebra or the relational calculus (Ullman [1982]). The relational cal-
culus is a variant of the predicate calculus with queries being open formulas of
the language. Formally, by the answer to a query Q(x) in the database DB
(which is viewed as a first order theory, a combination of database extension
and intension), we mean the set of all substitutions of domain constants for the
variable χ such that the resulting formula is a semantic consequence of the
database DB. If the databas ...