I found solution here :)
http://docs.jboss.org/jbpm/v5.4/userguide/ch.domain-specific-processes.html
One more intuitive way and less error-prone to define work items (JBPM term for what i was trying to create in this discussion) is to use the web-based designer. I could create new work items without handling configuration files under META-INF (designer tool does this for us) :)