Ideas and facts are not "copyrightable." But original expressions of ideas and facts are.
What are ways to upgrade open data so that copyright can be obtained on the database? Things that I can think of include formatting, presentation, aggregation, analyzing, etc.
What have users done with open data to make it sufficiently "original" in this way? For instance, does upgrading the data to five star data (linkable to other people's data) qualify?