There's no location info in a checksum. Now we want to be able to get location info out of the identifier. Checksums don't help. I'm not clear on this at all. What we're relly looking for is some client software that interprets these numbers and queries servers.
Checksums look as good as anything again.
If that's what we want, the checksum idea is no good. Until this item, it appeared that a document was a file. Now it's not so clear. Perhaps a document should be anything from a single character to a paragraph to a file to a chapter to a book to an encyclopedia to a library. That would be a good trick.