Note that we are talking about Task Server and there are more data you can access in regular queries on data base.
If it comes to the exposing jBPM specific information, I don't think you can completely avoid that. One thing you could query on is processInstanceId that is stored in the task server. Depending on your process definition it could be that at a given point in time only one task will be created for process instance id.
In addition to that, you could use task comments to place some meaningful information that would help you to find the right tasks.
HTH
P.S.
Here is a nice overview of the data base schemas for the engine and task server:http://community.jboss.org/message/627783