isknown
The
isknown 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 isknown);
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 true because a Java attribute of a Java class is always considered initialized.
Example
rule TestknownValue {
when {
?u: User(address isknown);
}
then {
sendToAddress(?u.address);
}
};