A DSAPI filter is built as a shared library, for example, as a DLL on the Windows platform. Since the filter is written in C, you can use the Notes C API to access Domino data or other C interfaces to access other systems.
DSAPI is supported on all Domino server platforms.
See the r5 release notes under 'Domino Web Server API (DSAPI)' for more info.
Example : FilterLibrary=c:\mvs\MyProjects\dsapi_sample1\Release\dsapi_sample1.dll