 Data format interoperability

Data format interoperability means that independent producers and consumers can exchange data with an agreed interpretation. Sharing a syntax is one part of that agreement; character encoding, supported values and handling of ambiguous inputs also matter. Serialization and deserialization must preserve the distinctions the application needs.^[ref]

Consider the original JSON input {"mode":"fast","mode":"safe"}. RFC8259 says object member names should be unique and warns that duplicate-name handling differs. In Python, the default json.loads result is {'mode': 'safe'}. The same decoder with object_pairs_hook=list instead returns [('mode', 'fast'), ('mode', 'safe')], preserving both pairs.^[ref][ref]

The text has not changed, yet one consumer retains one value and another retains both occurrences. Re-encoding the default dictionary cannot recover the discarded occurrence. A consumer can instead use a hook that rejects a repeated name, making the ambiguity explicit before the application acts on it.

An exchange contract can therefore require unique names and a shared duplicate-rejection policy, as well as a character encoding such as UTF-8. That is a stronger agreement than merely saying that both programs support JSON. Data validation then checks application-level requirements on the agreed decoded representation.