How to set up SAP BC for inbound URL/XML

Our customer wants to send us orders in cXML format via http/URL.
I am a newcomer to this sort of thing. I have set up BC to send invoices in cXMl via http/URL to the customer. Now I have to to the reverse - receive xmldata and map it to an idoc and post into SAP. Am I right in thinking that it should be possible to do do something like :

http:/sapbc001:5555/orders.incoming/PostOrder?xmldata=<xml version=“1.0” encoding=“UTF-8” ?>……

i.e the flow service POstOrder is called to map the the xml to the orders02 idoc format and post to SAP.

I have read the documentation (Adapter guide etc) but it is not very clear on what to do.

I can do the xml conversion/mapping/post etc but I am not sure what steps I actually need to do in SAPBC to execute a flow service from an http and get the xml.

i.e what I want to do is the inbound version of pub.client:http

Any help would be much appreciated.