In database configuration, create a relationship from PMFORECAST to JOBPLAN. In my example I created one called EMXJOBPLAN. The relationship should be:
jpnum=:jpnum and ((orgid=:orgid and siteid=:siteid) or (orgid=:orgid and siteid is null) or (orgid is null and siteid is null) or (:orgid is null and :siteid is null) or (:orgid is null))

Then in Application Designer, reference your relationship like EMXJOBPLAN.DESCRIPTION. I did a quick test and this worked for me.
