You must have a transformation model file open. A transformation model file has the name transform.tma.
By invoking XPath functions in an XPath expression, you can create calculations of greater complexity for a derived attribute. You can use derived attributes in XPath expressions in the same way that you use regular attributes.
You can create derived attributes in the editor area, in the Transformation input schema and output actions pane. You can also create them as part of the process of replacing text with a model reference.
To create a derived attribute for a JET transformation: