They are similiar but very different technologies. Astoria or what is now called at Microsoft ADO.NET Data Services is a programming library that will allow data to be passed through RESTful web services. You develop these web services to be run against data you have access to. ADO.NET Data Services is now included in the .NET 3.5 SP1 updates.
SQL Server Data Services is a new service provided by Microsoft. The following is a decription:
“SQL Server Data Services (SSDS) are highly scalable, on-demand data storage and query processing utility services. Built on robust SQL Server database and Windows Server technologies, these services provide high availability, security and support standards-based web interfaces for easy programming and quick provisioning.”
SQL Server Data Services is very similair to Amazon S3 service.
