When building less complex services, your BPEL process often uses input and output that is pretty much like the request and response on the wsdl. We would still want to decouple using the mediator component, so there is an extra transformation there which is pretty straight forward.
Sometimes it can be useful, easier and faster to use a assign in the mediator instead of a transform.
Imagine an pretty straight forward xsd:
I created an example BPEL process, also pretty straight forward. The Person is both the input and the output, all the BPEL process does is copy the input to the output and reply it:
In the Create Web Service dialog we create a WSDL based on the same XSD, also with a Person as input and output:
As said, because of decoupling, we would still want to have a mediator between the exposed service and our bpel process. We create a mediator and wire it both to the service and to the bpel process.
However, when editing the route, we usually use a transformation to map the input to the output, in this case, we are going to use an assign:
When you click the assign button, this also pop ups and Assign Values dialog, here we can wire the input element to the output element:
This way we use an assign in the mediator instead of creating an xsl transformation for this pretty straight forward transformation.