The official announcement of the new relational features that are coming to SQL Data Services:
What does this mean for developers? Developers will be able to very easily provision themselves a logical server and database and begin developing against it immediately using the existing tools and technologies that they are accustomed to. We are providing an experience where a developer can take an existing application and just change the connection string to point it to the cloud and have it just work.
How will we do it? Three letters TDS. TDS stands for Tabular Data Stream and it’s the published protocol that clients use to communicate with SQL Server. From its inception, SDS has always been built on the SQL Server technology foundation and it just made sense to allow our users to access their data via TDS. Most importantly for developers, this means symmetric SQL Server functionality and behavior combined with compatibility with the existing tools you are familiar with.
Visual Studio Compatibility?…Check
To be clear, the above is not a complete list of supported features.
read the etire post here: http://blogs.msdn.com/ssds/archive/2009/03/10/9469228.aspx