I'm a little bit confused about how jBPM really works.
Is there a databse behind the engine that handles all the processes? What Db is it?
Your confusion could be prevented by reading the documentation of jBPM, at least the first few chapters. Makes me wonder though how you got confused. All these questions will be answered then.
- yes (but it depends on whether you use jpdl, bpel or pageflow)
- all rdbms supported by hibernate