Hello Peter,
You can read about the Adagio database
here in the section on MS SQL compatibility.
Generally, it is irrelevant to the accounting department what database is in use, in the same way that the programming language is beside the point if the source code is not available.
I'm always curious when people ask this question. What prompts the inquiry? Are you looking a closely integrating some application with Adagio? If so, we'd be happy to provide guidance.