Extend common metadata by keywords

[m-mohr]

We've already made license and providers common metadata, but there are a couple more things that we could add there so that they get more "common".

• keywords from the Collection spec is general enough and could be useful elsewhere.
• language from OGC APIs: http://docs.ogc.org/DRAFTS/20-004.html#collections-properties-table, see also Multi-language support: add a property "language" to common metadata #1190
• A potential new bands field could replace eo:bands/raster:bands.
• We could also look at some of the prefix-less fields from the timestamps and version extensions.

[KennSmithDS]

@m-mohr emphasizing from prior discussion on Slack that Common Metadata get applied to Catalog objects as well, particularly keywords, created, updated.

[emmanuelmathot]

Totally agree with all the propositions. We could make separate PRs to propose and decide for each of them? I already did the work for keywords in this extension proposal: https://github.com/stac-extensions/subjects

[m-mohr]

Yes, we can sure go on a 1:1 basis. Keywords is meant to stay free-form without vocabulary though so I still think there's value in the subjects extension (although potentially aligned with OGC APIs).

For OGC APIs we also discussed (and agreed on) having created and updated in links as they don't have assets.

[p1d1d1]

could you please consider this? #1190

[m-mohr]

keywords: Wait for #1199 to be merged, then we can PR it into common metadata and directly remove keywords from the collection schema, too.

language is now part of the langauge extension: https://github.com/stac-extensions/language

[PowerChell]

The scope of this issue has been updated to the remaining issue: adding keywords to common metadata.

Update determined during STAC Working Session April 4, 2023.

[emmanuelmathot]

keywords: Wait for #1199 to be merged, then we can PR it into common metadata and directly remove keywords from the collection schema, too.

#1199 is not a PR. I dont find one that covers the keywords integration in common metadata

[m-mohr]

Yeah, the reference is off. I need to create a new PR for keywords.

[emmanuelmathot]

ok. I can help with that if needed.

[m-mohr]

@emmanuelmathot Great, happy to review the PR.

I guess it's relatively simple, just add keywords to the Basics category: https://github.com/radiantearth/stac-spec/blob/master/item-spec/common-metadata.md#basics
Update JSON Schema (move from Collection to common metadata and reference it from the Collection).