compare to SenML

[VladimirAlexiev]

https://www.rfc-editor.org/rfc/rfc8428 is an August 2018 by the IETF that claims to be fairly popular.
It defines JSON and CBOR (and XML and EXI) representations of time-series, and strives for economy of representation, eg here are two temperature readings of the same sensor:

 {"bn":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09, "v":23.5},
     {"u":"Cel","t":1.276020091e+09, "v":23.6}

[kenwenzel]

We've also played with shortening attribute names to t and v. In the end it helps a bit but in combination with GZip the current encoding ist also small enough.
But nevertheless I will take a closer look.