e.g. [iris](https://archive.ics.uci.edu/ml/machine-learning-databases/iris/) hosted on UCI e.g. [publaynet](https://dax-cdn.cdn.appdomain.cloud/dax-publaynet/1.0.0/PubLayNet.html) We can do this by just allowing the `download_url` field of schemata to accepts arrays.
