Microsoft will expose the network protocol from its SQL Server database as the service protocol in SDS (SQL Data Services), the cloud-based version of the database, thus enabling customers to use a full relational model in the cloud.

Under the plan, use of the TDS (Tabular Data Stream) protocol also will enable customers to leverage investments in T-SQL (Transact-SQL) development. Applications communicating with SQL Server send T-SQL statements to the server, Microsoft said on Tuesday.

SDS with TDS support is planned for release in a public CTP (Community Technology Preview) in the middle of this year, with commercial availability slated for the second half of 2009. A CTP of SDS was made available last fall.

SDS is a key piece of the Azure Services Platform for cloud computing, first revealed by Microsoft in October 2008.

"Over the last 4 months, SDS early adopters have been working with our REST service interface with its flexible entity-based data model. While we've received a positive response on that model, we have had significant feedback asking for more direct relational database capabilities, such as SQL queries, relational schema, and stored procedures," the company said in a post on the Microsoft SQL Server News Blog.

The company is accelerating delivery of relational capabilities in SDS through use of TDS. "With this evolution, SDS will become the first relational database service in the market to provide customers with the ability to use existing investments in T-SQL development and use a full relational data model in the cloud," Microsoft said in the blog.

SDS will enable developer "agility" and quick time to market by supporting use of existing applications, tools and knowledge while benefitting from distributed, cloud-based functionality, Microsoft said.

"This strategy enables customers to use a relational database service for their applications built on the Azure Services Platform," Microsoft said.

With acceleration of the T-SQL-based model, Microsoft will migrate from its current SOAP- and REST-based Authority-Container-Entity data model. Customers who want to expose REST-based access to SDS relational data can build custom services with ADO.Net Data Services, Microsoft said.

Azure users who want to use REST and whose needs are met with non-relational structured data storage can use Windows Azure table storage. Microsoft plans to announce technical details of the TDS-based SDS service at the Mix09 conference in Las Vegas next week.