[Zope] - Dynamic database of documents?

My current project involves the maintenance of a database of documents. The documents are split up into a tree structure and each entry in the tree is editable. In Bobo-land (which is where we're developing the application until I understand Zope enough to move there) we just have a heirarchy of objects that reflect the contents of the database. This exposes itself as a URL of: docs/DID/MID/TID/edit for the edit method of the Topic entry given by the ID from the database, TID. MID and DID are the Module ID and Document ID. Problem is, I can't see a way of getting Zope to do the DID part of the URL. That is, have a folder ID that is dynamic (I _think_ that's what I mean ;) Richard