A few years ago, we published an article which drew a formal analogy between chemistry and iTunes (sic)[cite]10.1021/ci060139e[/cite]. iTunes was the first really large commercial digital music library, and a feature under-the-skin was the use of meta-data to aid discoverability of any of the 10 million (26M in 2013) or so individual items in the store.‡ The analogy to digital chemistry and discoverability of the 70 or so million known molecules is, we argued, a good one.