The example that i can think of is the workflow of documents. list of users, list of documents and list of document types, each user can
send a document to one or more users receive a document reply to a document (sent doc is linked to the received one) forward the document comment on a document sign a document approve or disapprove a document document types have variable layout some document types have list of items the approval/disapproval can be at the document level or the item level I think schema-free is the most appropriate one for the example. --
