schema A reaction record in the ORD is structured as a Reaction message using Google's Protocol Buffers, which can be faithfully converted to and from JSON format without loss of information. For a specific Reaction, we focus on four chemically important fields: inputs, conditions, workups, and outcomes, each of which is also a message or a list of messages defined in ORD schema. An example reaction record is shown in Figure with representative fields populated. There are more than 600 fields defined in ORD schema, some of which are size-mutable, and an ORD record typically includes many nested messages. There are also strict rules on types and values admitted by data fields. For example, the type field of ReactionWorkup is an enum field that only accepts specific strings, and assigning out-of-vocabulary strings to this field leads to a syntactically invalid ORD record. The full definition of the Reaction message used in this study is available on GitHub.