Trademark A relational database management system from Microsoft. It originated in Sybase SQL Server, which was ported to IBM-compatible computers in 1989 by Sybase, Microsoft, and Ashton-Tate. Joint development by Microsoft and Sybase continued until 1994. Since then their products have diverged, with Microsoft developing for Windows while the Sybase version—renamed Adaptive Enterprise Server—is predominantly used on UNIX. SQL Server is now one of Microsoft’s flagship products.