Parsing the xml message and then identifying which method to use in XI??

In our scenario SAP XI need recieve and send message to third party .These xml messages use Document/Literal and therefore are not using any direct method calls. The broker(third party) will receive a document/literal messages and will forward this message to the given recipient(SAP XI). The recipient(XI) will need to parse the message, dissamble it's parts and will call the appropriate method in the business layer. In turn, a response message is send.

Which method eventually will be called is determined by the root element of the Soap messages body. For example msg04 has the root element vchmsg04. After receiving the message, the method vchmsg04 will be called.

Can you please help us or guide us on how this can be achieved??