InChI Key is an example of #2 that does not imply #1. For a variation on the theme, if we all agreed on a canonical SMILES method, then the SHA256 of that coul

InChI Key is an example of #2 that does not imply #1. For a variation on the theme, if we all agreed on a canonical SMILES method, then the SHA256 of that could be used as a key to connect records, without revealing what the underlying structure is. This is done now, with InChI Key, when two companies want to compare overlap without sharing information about internal compounds. (There was a paper about this last year or so, but I can't find it.) I also pointed out that InChI Keys are better for text-based search engines. As an extreme example, I could produce a line notation which uses only the characters "(", ")", ".", and "-". It would be fine for #1, but poor for #2 for any database search engine which expects some concept of "words" made of letters. This is why I distinguish #1 from #2, even though they are indeed close.