Open Source Document Management System | OpenKM

I want to use open KM api for creating chat and discussion forum functionality in my application.
Please tell if it is possible to use the api for these functionalities. Also if yes, then how to use these api. How have they been exposed?

That's a very strange use of a DMS, consider using thirdparty apps for it, specialized to forum and chat.
Forum is a module that has not exposed API acros webservices. The same with chat.