Boolean conjunctive query
Encyclopedia
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?"
Conjunctive query
In database theory, a conjunctive query is a restricted form of first-order queries. A large part of queries issued on relational databases can be written as conjunctive queries, and large parts of other first-order queries can be written as conjunctive queries....
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 arityArity
In logic, mathematics, and computer science, the arity of a function or operation is the number of arguments or operands that the function takes. The arity of a relation is the dimension of the domain in the corresponding Cartesian product...
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?"