Changes to item properties

[dchandan]

Proposing a few changes to the schema:

1. Changing cmip6:realm and cmip6:source_type to be types arrays rather than strings. Some CMIP6 variables can belong to more than one realm and more than one source type.
2. Adding an optional cmip6:version property. Although this is not a required global attribute, it does form an important part of the DRS and "used for example, to construct file names, directory structures, the further_info_url, and in facets of some search tools" (Data Reference Syntax (DRS) components). Since this property helps distinguish between more than one versions of the same file on the ESGF nodes, it can be used for the same purpose on STAC catalogs. Though I think this ought to be a required field in the extension, since this is not a required global metadata field in ESGF data files and would therefore need to be determined indirectly, I would be content with the property being optional.

[TomAugspurger]

Thanks for the PR!

I generated this item from the file at https://rhgeuwest.blob.core.windows.net/cil-gdpcir/CMIP/BCC/BCC-CSM2-MR/historical/r1i1p1f1/day/tasmin/v1.1.zarr

In [24]: r = requests.get(planetary_computer.sign("https://rhgeuwest.blob.core.windows.net/cil-gdpcir/CMIP/BCC/BCC-CSM2-MR/historical/r1i1p1f1/day/tasmin/v1.1.zarr/.zattrs"))

In [25]: data = r.json()

Is it fair to say that that metadata isn't compliant with CMIP6?

[dchandan]

Yes, I am inclined to think so. According to Table 1 from the DRS document it seems realm and sourece_type could take multiple values and that's what I've seen in the metadata of some model outputs.

[dchandan]

Any thoughts on this @TomAugspurger?