Variable declarations

You can use transformation variables in order to keep values that you plan to reuse later. For example, if calculation of a value takes time it might be more efficient to create a transformation variable for the value and then reuse this variable. See Using local variables in transformations.

A variable is introduced in the current evaluation scope, and its corresponding XPath expression is evaluated. All variables are evaluated in the declaration order, but after the host element evaluation.

<tdt:rule path="/data/day"> <!-- variables are evaluated in declaration order --> <tdt:value key="$hello">'Hello'</tdt:value> <tdt:value key="$world">'World'</tdt:value> <tdt:value key="$greeting">concat($hello, ' ', $world)</tdt:value> <!-- No access to variables(host evaluated before) --> <tdt:value key=".">...</tdt:value> </tdt:rule>

When you define a variable for an element, its value can be used in the element and in all its descendants (not in siblings or parent elements). You can re-define the variable on each descendant level, but you can only define it once at each level. If you re-define the variable on a child element, the new value is used in this scope. Outside this scope, the value of the parent is used.

<tdt:rule path="/data/day/station"> <!-- Access to variables from '/data/day' rule ($hello, $world, $greeting) --> <tdt:value key=".">...</tdt:value> <tdt:value key="$greeting">concat($hello, ' beautiful ', $world) </tdt:value> </tdt:rule> <tdt:rule path="/data/day/station/name"> <!-- Here $greeting equals 'hello beautiful world' --> </tdt:rule> <tdt:rule path="/data/day/conclusion"> <!-- Here $greeting equals 'hello world' --> </tdt:rule> <tdt:rule path="/data/night"> <!-- Here $greeting is not accessible --> </tdt:rule>