Database Engine Extended Stored Procedures - Reference
Applies to: 
SQL Server
Important
This feature will be removed in a future version of SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. 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.
Important
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.