[arata]

> What character decomposition database is this using..

From the about page, it seems that it's using Wikimedia data: https://commons.wikimedia.org/wiki/Commons:Chinese_character... .

To add to your comment, there's also RADKFILE/KRADFILE, which is used by a lot of Japanese dictionaries out there (including jisho.org), and also IDS (Ideographic Description Sequence) data: https://github.com/cjkvi/cjkvi-ids . The latter, I believe, is not meant for general lookup, but nonetheless can be quite informative, such as identifying semantic/phonetic components.