After adding the new history columns introduced in JBPM-2398 to the create/drop schema scripts and reviewing the QueryOperand use, I am not very comfortable with the fact that the parameter value has to be a String, even if operands such as IN should be taking a List. I'd much rather have a factory for restrictions that can be added to queries much like the Hibernate criteria API. Unfortuantely when reaching that level of flexibility one begins to wonder why not just skip the jBPM queries entirely and go straight to the far more expressive Hibernate criteria. I will reopen JBPM-2873 and work on this proposal. Excuse me if I did not chime in earlier.