All implementations of Windchill that use WTParts and EPMDocuments will also use WTDocuments, there is a lot of inconsistency in the product here and much confusion for users. "But its a document too, why is it different?". Some more specific examples.
WTDocument relationships are managed from the WTPart and require checking out the WTPart
EPMDocument relationships are managed from the EPMDocument, even though you have to checkout the WTPart to edit them
There is nothing to indicate if a build rule has been built or not.
The Association Types are unclear and confusing. An Image association does not pass a representation
My suggestion is to combine all the document object relationships into a single table, with a common toolset for managing the relationships to WTParts. This would include some new and clear functionality around what the various build rules do, as well as the ability to pass additional information from WTDocuments. The attached screenshot mock up hopefully illustrates the kind of thing I am imagining.
This idea relies on some other product ideas I had submitted previously: