Declare a variable in query prolog.
A VarDecl declares a variable along with an optional type
information in the prolog. It contains the keywords declare
variable, followed by the variable name. An optional type information is
introduced by the keyword as. The final keyword
external is mandatory and indicates that the value of the variable
will be provided by the external environment of the query. A type error is
raised if in the dynamic phase of query processing the value is not of the
specified type. If a variable declaration does not include a type declaration,
then item()* is assumed.
Please note that a variable declaration differs from a variable binding
as performed by for and let in FLWOR expressions. A
variable declaration always refers to the declaration of a variable in a
prolog, while a variable binding binds a variable to a value in a query
expression and does not make the variable visible in the importing module.
This variable declaration declares the variable
$x as of type integer:
declare variable $x as xs:integer external
This variable declaration declares the variable
$x. As type item()* is assumed:
declare variable $x external
The following construct(s) refer to this construct:
This construct is also related to the following construct(s):
See also the discussion of external variables in the section
The _execute
command of the X-Machine programming documentation.