That does sound like a great idea.
I have one, also. But, I believe it will take quite a bit of 'coding' to pull it off.
My idea is a search query in conventional database only by frequency and PL/DPL information. 2 user 'fill-in' boxes and a drop-down for PL or DPL choice. Or, possibly eliminate the drop-down all together since not all data in the RRDB has a PL/DPL after it.
Just a thought.