isunknown
The
isunknown keyword tests whether a
class attribute has an initialized value.
Purpose
This keyword is used in the condition part or in the action part of a rule or in a function to test whether the attribute has a value.
Context
Any expression
Syntax
[?var:] className (?attribute isunknown);
Description
In the case of XML binding, an attribute has no value in the following cases:
When the value is not given in the XML file, or
When the value is given in the XML file and set to
xsi:nil.
In the case of Java™ classes,
the test always returns false because a Java attribute of a Java class is never considered as not initialized.
Example
rule TestUnknownValue {
when {
?u: User(address isunknown);
}
then {
askForAddress(?u);
}
};