Although there have already been public betas of Microsoft's new relational database, most notably one launched last February, the latest release candidate lets you reliably test the development environment's most critical new feature.

Had all gone as planned, SQL Server 2008 would have been one of the stars of last February's "Heroes Happen Here" rollout of Microsoft Enterprise products in Los Angeles. As it turns out, the sequel of that launch took place this morning in Orlando, during platform division president Bob Muglia's keynote speech to the IT professionals' half of Tech·Ed: The company's next relational database engine has now exited beta, and is at Release Candidate 0 (all of Microsoft's RCs now start at zero).

The new release candidate features the modified SQL Server Management Studio, which with this release adds policy-based management. Policy is fast becoming a part of every Microsoft administrative tool. In this case, policy lets the database administrator create enforceable rules, which the Management Studio can explain in English or the users' native language. Microsoft introduced this concept a few years ago as the Declarative Management Framework (some developers still refer to it as DMF), in add-on products to SQL Server and SQL Server Express.

In a recent MSDN screencast (WMV video available here), solutions advisor Bryan Von Axelson demonstrated DMF using an earlier beta of the SS 2008 engine. Every database object now can have a policy associated with it -- a rule which governs how it can be used. To create a policy or edit an existing one for an object, you right-click on that object in Object Explorer, and select the option from the popup menu.

From there, you're taken to a rules panel that goes into further detail. For instance, you can run a policy at will on any object to test it out -- like a live query -- and obtain a result as a database table.

One example Von Axelson showed involved making sure the database schema under which a new table is created, follows a prescribed template. If the schema doesn't exist, table creation can fail -- and that "fail" is a good thing, because that stops the dissolution of the main database schema.

DMF is a feature of the main SQL Server 2008 RC0 package, and is intentionally omitted from the scaled-down SQL Server 2008 Express release candidate package -- also unveiled today.

Testing a database release candidate is a very tricky thing, so using a virtual machine is critical. You'll want to use a mature SQL Server 2005 database, but you don't want to destroy it, either. So the secret is copying a volatile version of the 2005 version into a virtual environment, and then converting it to 2008 specifications. That's not an easy affair in and of itself, and some Microsoft developers are actually suggesting the use of a third-party translation tool already available called SQL Server 2008 Upgrade Assistant, from a company called Scalability Solutions.

Your development system will need to be upgraded to handle SS 2008, even if you just got your new copy of Visual Studio. VS 2005 users will need to download and install this Visual Studio 2005 Support for SQL Server 2008 add-on, which adds support for debugging both T-SQL (Transact-SQL, a set of transactional conventions supported by Microsoft and Sybase) and SQL CLR, the common language runtime edition of SQL under .NET.

Still, that won't give you everything, such as the ability to use the new Table Designer feature to render a new table or schema -- that's for people who upgrade their Visual Studio.

But Visual Studio 2008 users must apply updates as well. Thankfully, they're free. New IDE users will need to install Visual Studio 2008 Service Pack 1 Beta, which adds not only support for SS 2008 but also improvements to handling of the .NET Framework, and added support for newer versions of Silverlight. Users of any of the Express (free) editions of Visual Studio have their own update they'll need to apply, and that's officially a beta as well.