Hi Jeff,
Thanks for the explanation Jeff. I'll try to test this idea when I get the time soon.
But let me see if I understood it correctly. Please be patient since I'm really a newbie with regards to using the DI Server, XML, soap calls, and DI API SDK(where the DI Server is a wrapper for). 
So when converting lets say a couple of Sales Orders into an A/R Invoice, following what you said from your reply, when I commit or send the Create SOAP call for the invoice with linked Sales Order Entries in the DocumentLines like the one below
<dis:Add xmlns:dis="http://www.sap.com/SBO/DIS"> <Service>InvoicesService</Service> <Document><DocumentLines><!-- Some lines with BaseEntry, BaseLine, BaseType based on Sales Orders --> </DocumentLines> </Document></dis:Add>
When successful, the Sales Orders will be in a way converted to A/R Invoice?
Happy New Year!