REST style web services for data access. By REST style, that means using HTTP GET/PUT/DELETE/POST instead of SQL DML, and for returning results it uses JSON and Atom Pub (an xml format kind-of similar to RSS) instead of a binary result structure and protocol like Microsoft SQL Servers TDS (the protocol used for sending tables back to clients).
Since it is built on top of the Entity Framework,i.e. the web service part is generated from a edmx data model, choosing to use ADO.NET Data Services is also choosing to use Entity Framework.