A web data service, such as the Astoria web data service that you are able to create using the Astoria CTP, is a specialized form of a WCF web service that is fully aware of the nature of the data that is exposing. Being "data aware", the service able to provide additional opperations that would not be available through a general web service, such as paging.
Anonymous563494 wrote:
what's the difference between web data services vs web services
I would argue there is no difference. Every web service provides data. I guess if you're looking for an accepted description then Elisa's will suffice.
-Jamie