Passing Infopath form fields to a workflow being called using web services

I am creating an Infopath form which calls a Site Workflow using web services.  The web call works fine and I am able to pass data defining the data fields manually to the started workflow   i.e. 

<Data>

<MyVal1> some random data </myVal1>

</Data>

Does anyone have an example of how I can pass the field values from the Infopath form to the workflow?  I need to substitute the literal data with field values.