Approach to atompub implementation for a forum

[Ivan Sagalaev <maniac@xxxxxxxxxxxxxxxxxxx>]

Hello!

I'm playing with an idea of implementing AtomPub for my forum and I'm a 
bit stuck choosing a right architecture. The forum site contains several 
forums which contain topics which contain articles -- a simple hierarchy.

First I figured out that individual forums should probably be 
Collections in AtomPub terms. But as far as I understand a Collection 
can contain only Entries which themselves cannot be Collections 
(right?). So then I stuck how to describe topics in forums and, further, 
articles in topics.

Another approach is to represent topics as Collections of articles. 
Forums can be Workspaces containing topics. But then I have an 
ever-growing Service document that would describe topics-Collections.

Please share any advice! Thank you.