> <i>at least not until the IANA get around to officially assigning them a media type.</i><p>This is the wrong characterisation. IANA does not take such initiative; their role is administrative rather than regulatory or active. It’s up to an interested party to register media types.<p>For Parquet, that’s easy: the developers can fill out <a href="https://www.iana.org/form/media-types" rel="nofollow">https://www.iana.org/form/media-types</a> in probably less than ten minutes, probably choosing the media type application/vnd.apache.parquet. It’ll be processed quickly.<p>For JSON Lines/NDJSON, it’s messier, calling for standards tree registration, which generally means taking a proper specification through some relevant IETF working group. (There are a few media types in customary use presently, all bad: application/x-ndjson, application/x-jsonlines, application/jsonlines; all are in the standards tree despite nonregistration, and two include the long-obsolete x- prefix.) Such an adventurer will doubtless encounter at least some resistance due to the existing JSON Text Sequences (application/json-seq, defined in RFC 7464, <a href="https://www.rfc-editor.org/rfc/rfc7464" rel="nofollow">https://www.rfc-editor.org/rfc/rfc7464</a>), which is functionally equivalent, mildly harder to work with, and technically superior, due to being unambiguously not-just-JSON, using a ␞ (U+001E RECORD SEPARATOR) prefix on every record, but given the definite popularity of JSON Lines/NDJSON, an Internet Draft will easily be enough for provisional registration.