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Conditions are used to control when particular rules can be fired. Each condition contains an XPath to evaluate against the FactBase. The condition will be true if this XPath returns a 'true' value.
For the purposes of condition checking, an XPath will be considered 'true' if:
It evaluates to a non empty node set. It returns the boolean value 'true'. (e.g. from using the not() function) It returns a string which does not have the text value 'false'
Condition image Each rule can have a simple condition (with just one XPath check), or it can be complex, with a number of conditions joined through boolean operators AND, OR, and XOR. It is also possible to have a rule without a condition section, in which case the rule will fire as soon as it has the highest priority.  
Constructing Rules Simple Conditions