The Library of Congress has reorganized its site on file format sustainability and given it a new URL. (The old one redirects there.) A blog entry discusses the change. Relationships among formats are a big part of the site. It’s significant, for instance, that the MP3 encoding and the de facto MP3 file format get separate entries.
My reactions are mixed. When you click “Format Descriptions” on the main page, you get a page titled “Format Description Categories.” The nesting description at the top says you’re in “Format Descriptions as XML.” Eight categories are listed, and two formats plus “All xxx format descriptions” are listed under each category. There’s no obvious reason why those two formats get special prominence, or what the page has to do with XML.