Hi,
Using DataService is no longer recommended in latest SDK versions but is heavily used and still supported.
The API documentation is part of the SDK deliverable and is located at html-client-sdk/docs/javadoc/index.html
This is the latest online documentation link with regards to DataService usage: Developing Extensions to the Service Layer
For some sample code please check QueryUtil class in the HTML Bridge samples part of SDK 6.5U1 (which is the latest version that has the Bridge samples).
Hope that helps.
Cheers,
Vladi