The top part (diagram) should be updated automatically not with "Parse Query"
button. Just imagine that you would need to call a Parse Source action in Java
if you wanted to see the errors!! The parser does not need to be incremental,
IMHO, and even w/o decent error recovery it is probably OK. Performance analysis
will of course be needed and it should be started periodically after a given
timeout. If there is an error while the user it typing then of course do not
update the model, display error in error annotation and wait until it's parsed
w/o errors.
BTW, "Parse Query" may not be the best name, it's a bit geeky IMO, better call
it "Refresh Diagram" or something like that. But ideally this action should not
be needed.