Some thoughts

[schwehr]

This is my comment on https://gitter.im/SpatioTemporal-Asset-Catalog/Lobby?at=62b41f1a568c2c30d3dfa48b

It seems like there should be an explanation of how this relates to the existing keywords field and how it relate to other ontology schemes. I've been wanting to have a glossary type section parallel to an existing catalog that has a STAC Catalog for each keyword that explains the keyword and links to all the STAC Collections / Items that have that keyword (the Earth Engine catalog is currently completely static). How might that idea relate?

[schwehr]

https://github.com/radiantearth/stac-spec/blob/master/collection-spec/collection-spec.md#collection-fields

Existing keywords:

Element	Type	Description
keywords	[string]	List of keywords describing the Collection.

[emmanuelmathot]

ok I see the ambiguity here. The idea is to have a space for free keywords without any reference. Pretty much as tags. Terms are bond to a reference system. Initially, there are no links intended here between the 2 fields. I'd like a system easy to implement and quick for searching in STAC API. I think there are enough ontology reference system to tap into but we could imagine the reference system pointing to a local existing catalog.

[m-mohr]

I'm still a bit confused.

You said:

The idea is to have a space for free keywords without any reference. Pretty much as tags.

This is exactly the purpose of the STAC Collection keywords field. How it the keywords fieldhere and in the Collection different? And if they are different (which I assume), I think it would make sense to use another field name to make the difference clearer.

What I'm also wondering about is whether you could re-use keywords and just add the terms on top?

[emmanuelmathot]

Actually no differences with the field keywords of a collection except they apply to an item. We could extend the keyword field for the items. Nevertheless, the core of this extension is about system referenced terms with the field subjects:terms.

[m-mohr]

Yes, I think that is a good idea and would be very much in line with the common metadata model STAC is embracing. So generalize keywords for Items and Collections and then extend it. In that case, it might make sense to call the terms field something like "keyword:terms"?

[emmanuelmathot]

Indeed, it could. So could we keep it as an extension or make it part of the core spec?

[m-mohr]

They keyword list should be core spec, i.e. common metadata: https://github.com/radiantearth/stac-spec/blob/master/item-spec/common-metadata.md This is likely just a copy/paste from the Collection spec.

And then the separate extension would basically be the terms. But this is just my opinion right now.

[jjrom]

I agree with @m-mohr on the keywords for items. It should be in the core spec as a copy/paste from the collection spec i.e. a field named keywords

[schwehr]

Reading up on RDF and OWL2 was pretty frustrating.

This looks interesting: https://www.earthdata.nasa.gov/learn/find-data/idn/gcmd-keywords

e.g. ATMOSPHERIC OZONE

https://gcmd.earthdata.nasa.gov/KeywordViewer/scheme/all/dd316647-9043-40c3-9329-f22f9215fefa

ATMOSPHERIC OZONE

Full Path EARTH SCIENCEATMOSPHEREATMOSPHERIC CHEMISTRYOXYGEN COMPOUNDSATMOSPHERIC OZONE

UUID dd316647-9043-40c3-9329-f22f9215fefa

Category Earth Science

Earthdata Search Client

Definition

Atmospheric Ozone is one of the most important trace gases in our atmosphere that both benefits and harms life on Earth. High ground-level ozone amounts contribute to poor air quality, adversely affecting human health, agricultural productivity, and forested ecosystems. Ozone absorbs infrared radiation, and is most potent as a greenhouse gas in the cold upper troposphere located 8–15 km above the surface. In the stratosphere, between approximately 15 and 50 km above the Earth’s surface, a layer rich in ozone serves as a “sunscreen” for the world by shielding the Earth’s surface from harmful ultraviolet radiation. This absorption of solar energy also affects atmospheric circulation patterns and thus influences weather around the globe. Moreover, throughout the atmosphere, ozone is the key ingredient that initiates chemical cleansing of the atmosphere of various pollutants, such as carbon monoxide and methane, among others, which could otherwise accumulate to harmful levels or exert a stronger influence on climate. Therefore, changes to ozone anywhere in the atmosphere can have major impacts on the Earth.

Reference https://www.ametsoc.org/index.cfm/ams/about-ams/ams-statements/statements-of-the-ams-in-force/atmospheric-ozone1/

Broader OXYGEN COMPOUNDS

Narrower OZONE PROFILESOZONE SURFACETOTAL OZONE

[m-mohr]

Following OGC API - Records now, keywords is the free-form equivalent in STAC, see the corresponding PR in stac-spec.