stac-spec

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what would one do if an item belongs to multiple collections in a STAC? the collection field in the item spec is a string. if an item belongs to multiple collections would it be indicated in a list? or comma-separated string? and then what would one do with the rel:collection link? multiple instances? or one instance for one of the collections the item is in and then have alternates for the other collection memberships?

This "issue" has already been discussed in the past here. TLDR; You can have a single collection per item then. You can also have multiple collections pointing to an item, but a item can only point back to a single collection, which the item is "inheriting" from.

Other discussions about multiple parents are ongoing:

• https://github.com/radiantearth/stac-spec/issues/1236
• https://github.com/radiantearth/stac-spec/issues/1230

Somewhat related (hierarchical collections): https://github.com/opengeospatial/ogcapi-common/issues/298#issuecomment-2115855204 So something we should review.

The work that OGC is doing is purely relevant to APIs, we don't need to consider it in the static version of STAC.

The question has also been answered and the OP did not respond yet, so we assume that this issue has been clarified sufficiently. I'll issue a small PR to clarify the issue in the spec.

For me the issue may be closed. In our back-end we can handle an item being part of multiple collections (like views on a table). But when looking at an item from the view of a collection, it is just part (or not) of that one collection.