Database Engine Extended Stored Procedures - Reference
This feature will be removed in a future version of Microsoft SQL Server. Do not use this feature in new development work, and modify applications that currently use this feature as soon as possible. Use CLR integration instead.
The Microsoft Extended Stored Procedure API, previously part of Open Data Services, provides a server-based application programming interface (API) for extending Microsoft SQL Server functionality. The API consists of C and C++ functions and macros used to build applications.
With the emergence of newer and more powerful technologies such as CLR integration, the need for extended stored procedures has largely been replaced.
You should thoroughly review the source code of extended stored procedures, and you should test the compiled DLLs before you install them on a production server. For information about security review and testing, see this Microsoft Web site.