Expression Element (parmval Expressions)

The parmval expression allows access to the mapping rule’s parameters by referring to them by name in its expression string. The parmval expression is represented in xfMap by the <parmval> element; its expr attribute holds the value of its expression string:

<parmval expr="the-name-of-a-mapping-rule-parameter"/>

The actual value for a parameter in an activated mapping rule R1 must be supplied by a mapping rule R0, where R0 is the mapping rule that got suspended when R1 activated.

The expr value for the parmval expression may be optionally specified via a named argument. This allows the expr value to be constructed programatically by an expression sequence. The argument must be named ‘expr’ and it must take the following form:

<parmval><arg named="expr">...any expression sequence...</arg></parmval>

For example, the following mapping rule sets the feature type with a parmval expression:

<mapping match=’...’>
	<signature name=’myRule’>
		<params>
			<param name=”firstParam”/>
		<param name=”theFeatureType”/>
		</params>
	</signature>

	<feature-type>
		<parmval expr=”theFeatureType”/>
		<literal expr=”_”/>
		<parmval>
			<arg name=”expr”>
				<literal expr=”firstParam”/>
			</arg>
	  </parmval>
	</feature-type>
</mapping>