Imagine that your InfoPath form, which submits to DBXL, needs to make sure that there are no duplicate records. Using the web method QueryDocumentNodeSet, we can quickly check whether DBXL already contains a matching record.
For the purposes of this tutorial, we will implement the solution on a very simple form, though you can extend this as desired. You can download the PDF tutorial (13 pages, 950Kb) by clicking here.