Structure and the ability to maintain the Integration artifacts in any SOA development are as important as the artifacts itself. In my projects, I give a reasonable focus on the governance of the Integration artifacts. Technical Artifacts governance is subset of Overall SOA Governance.
XML Schema definitions
Web Services Definition Language
Cross References & Domain Value Mappings
How to structure the artifacts?
The following are the key things to consider while creating the integration artifacts.
Canonical Model (Customer, Product, Order, Invoice, Address, etc)
Application specific folders versus Common folders (EBiz, Siebel, SAP, Common, etc.)