Limiting mapping rule activation with except expressions.

A mapping rule can have one or more except expression. The syntax for except expressions in the <mapping> element’s except attribute is identical to match expressions, i.e:

(ancestorElement/)*element([booleanExpr])?
[<whitespace>(ancestorElement/)*element([booleanExpr])?]*

The except expressions are evaluated in order and a mapping rule R fails to match an element E if any of the except expressions in the mapping rule matches element E.

For example, consider the following rule XML file and mapping rule fragments:

<?xml version="1.0"?>
<family-tree>
	<grandparent> ...</grandparent>
	<grandparent> ...</grandparent>
	<grandparent> ...</grandparent>
	<grandparent> ...</grandparent>
	<parent>
		<name>Tristan Read</name>
		<gender>m</gender>
		<age>40</age>
	</parent>
	<parent>
		<name>Danielle Read</name>
		<gender>f</gender>
		<age>43</age>
	</parent>
	<child>
		<name>Grifffen Read</name>
		<gender>M</gender>
		<age>12</age>
	</child>
<family-tree>

Then the following mapping rule would match only the children and parents:

<mapping match=”family-tree/*” except=”grandparent”>
	...matches all family members except the grandparents
</mapping>

This is quite useful when it is easier/briefer to define a match set negatively (everything but ...) rather than positively (the match is a, or b, or c, or d, ...).