The Open Data Services API is a server-based API specific to Microsoft® SQL Server™. It can be used to produce two types of applications:
An extended stored procedure is a C or C++ DLL that can be called from Transact-SQL using the same syntax as calling a Transact-SQL stored procedure. Extended stored procedures are a way to extend the capabilities of Transact-SQL to include any resources or services available to Microsoft Win32® applications.
Gateways are server applications that allow applications written to access SQL Server to work with other databases. The need for gateway applications has largely been made obsolete by newer technologies such as SQL Server distributed queries, Windows NT Component Services, and general database APIs such as ADO and OLE DB.
Programming Open Data Services