In the theory of relational databases, a Boolean conjunctive query is a conjunctive query without distinguished predicates, i.e., a query in the form, where each is a relation symbol and each is a tuple of variables and constants; the number of elements in is equal to the arity of . Such a query evaluates to either true or false depending on whether the relations in the database contains the appropriate tuples of values.
As an example, if a database schema contains the relation symbols (binary, who's the father of whom) and (unary, who is employed), a conjunctive query could be . This query evaluates to true if there exists an individual who is a child of Mark and employed. In other words, this query expresses the question: "does Mark have employed children?"
Famous quotes containing the word query:
“Such condition of suspended judgment indeed, in its more genial development and under felicitous culture, is but the expectation, the receptivity, of the faithful scholar, determined not to foreclose what is still a question—the “philosophic temper,” in short, for which a survival of query will be still the salt of truth, even in the most absolutely ascertained knowledge.”
—Walter Pater (1839–1894)