Are there other resources on WS-CDL beside the spec and the primer?

Are there other resources on WS-CDL beside the spec and the primer?

For example as to what I am looking for - I read through the spec and the
primer and I can still not understand clearly what are the added value of
channels and relationships. Looking on the basic example in the primer,
specifically on the following two lines:

         <interaction name="QuoteElicitation" operation="getQuote"
channelVariable="tns:Buyer2SellerC">
            <participate relationshipType="tns:Buyer2Seller"
fromRoleTypeRef="tns:BuyerRole" toRoleTypeRef="tns:SellerRole"/>

It seems that these two elements only describe two more times that the
interaction is from a buyer to a seller, which is already specified by
stating the participants and their roles.

Can anyone point me to some reading material that will emphasize the
differences between the three declarations? maybe some examples? (or just a
reference into the spec that I missed or misunderstood?)

On a similar issue - is the primer not done yet? or am I looking on an old
version? The version I get from the working group site has empty
subsections. If it is not done yet, is there a newer version on the way?

Thanks,
Ouri.