Gareth,
Regarding the first mechanism you listed; Could you explain how the tagging in the XML documents can link to service parts within Windchill? Is there a feature in Windchill that looks at the xml instance, and relates the parts contained within an xml document to parts managed within windchill?
Additionally could you explain the Windchill "related objects" feature? any documentation on these features would be greatly appreciated.
I think you could do this via customisation,
I have browsed other threads regarding customization, I'm assuming this means writing what it referred to as ACL code/script or even JavaScript correct?
Thanks for the information you've provided thus far, I'm believe the picture becoming clearer.
-Steve