Safety of Expressions
The Tuple Relational
A tuple relational calculus expression is of the form
Several tuple variables may appear in a formula.
A tuple variable is said to be a
unless it is quantified by a
. Then it is said to be a
A formula is built of
. An atom is one of the following forms:
is a tuple variable, and r is a relation (
is not allowed).
are tuple variables, and
are attributes, and
is a comparison operator (
is a constant in the domain of attribute
are built up from atoms using the following rules:
An atom is a formula.
is a formula, then so are
are formulae, then so are
is a formula containing a free tuple variable
are formulae also.
Note some equivalences:
Page created and maintained by
Osmar R. Zaï ane
Last Update: Wed Sep 20 15:45:57 PDT 1995