Formal Definitions
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The Tuple Relational
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Example Queries
Formal Definitions
A tuple relational calculus expression is of the form
where
is a
formula
.
Several tuple variables may appear in a formula.
A tuple variable is said to be a
free variable
unless it is quantified by a
or a
. Then it is said to be a
bound variable
.
A formula is built of
atoms
. An atom is one of the following forms:
, where
is a tuple variable, and r is a relation (
is not allowed).
, where
and
are tuple variables, and
and
are attributes, and
is a comparison operator (
).
, where
is a constant in the domain of attribute
.
Formulae
are built up from atoms using the following rules:
An atom is a formula.
If
is a formula, then so are
and
.
If
and
are formulae, then so are
,
and
.
If
is a formula containing a free tuple variable
, then
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