How do Schemas support RDF collections?

Hello,

How do RDF schemas (DAML+OIL, RDFS, even OWL) support RDF collections 
(bag, seq, alt)?  I have a hole in my understanding of how to write 
OWL/DAML+OIL schemas that support Bags.

For instance, if I want to say:

User hasMemberships is a Bag.
Group hasMemberships is a Bag.
Bag is collection of Group resource URIs.

How would I use a Transitive Property in OWL for this:

If Bob hasMembership of Group X,
And Group X hasMembership of Group Y
THEN Bob is a member of Group Y.

(creating hierarchy of groups)

If create an explicit property hasMembership for users and groups, then 
it becomes easy.  Once I make hasMembership plural, then I'm getting 
lost as to how to specify those handy relationships when the resource 
I'm talking about is now a Bag.

Should the APIs for programming to these models make these collections 
transparent?  It makes it harder for me to ask questions when I have to 
manually check inside a Bag.

I'd like to have the APIs turn this:

User hasMembership Bag (content, content, content)

into

User hasMembership content.
User hasMembership content.
User hasMembership content.

That would make programming against the model graph a lot simpler.

What am I missing?  Am I making this too hard?

Any ideas or help would be greatly appreciated.  I'm using Jena and 
redland currently.

thanks very much,
Seth