diff --git a/catalog-spec/catalog-spec.md b/catalog-spec/catalog-spec.md index e457aad1..c918098b 100644 --- a/catalog-spec/catalog-spec.md +++ b/catalog-spec/catalog-spec.md @@ -85,13 +85,14 @@ For a full discussion of the situations where relative and absolute links are re The following types are commonly used as `rel` types in the Link Object of a STAC Catalog: -| Type | Description | -| ------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -| self | STRONGLY RECOMMENDED. *Absolute* URL to the location that the Catalog file can be found online, if available. This is particularly useful when in a download package that includes metadata, so that the downstream user can know where the data has come from. | -| root | STRONGLY RECOMMENDED. URL to the root STAC Catalog or [Collection](../collection-spec/README.md). Catalogs should include a link to their root, even if it's the root and points to itself. | -| parent | URL to the parent STAC entity (Catalog or Collection). Non-root Catalogs should include a link to their parent. | -| child | URL to a child STAC entity (Catalog or Collection). | -| item | URL to a STAC Item. | +| Type | Description | +| ---------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | +| self | STRONGLY RECOMMENDED. *Absolute* URL to the location that the Catalog file can be found online, if available. This is particularly useful when in a download package that includes metadata, so that the downstream user can know where the data has come from. | +| root | STRONGLY RECOMMENDED. URL to the root STAC Catalog or [Collection](../collection-spec/README.md). Catalogs should include a link to their root, even if it's the root and points to itself. | +| parent | URL to the parent STAC entity (Catalog or Collection). Non-root Catalogs should include a link to their parent. | +| collection | URL to a parent Collection. *Absolute* URLs should be used whenever possible. The referenced Collection is STRONGLY RECOMMENDED to implement the same STAC version as the Catalog. A link with this `rel` type is *required* if the `collection` field in properties is present. | +| child | URL to a child STAC entity (Catalog or Collection). | +| item | URL to a STAC Item. | **Note:** A link to at least one `item` or `child` (Catalog or Collection) is **RECOMMENDED**, but empty catalogs are allowed if there is an intent to populate it or its children were removed. diff --git a/collection-spec/collection-spec.md b/collection-spec/collection-spec.md index 7e1e7842..9a9438af 100644 --- a/collection-spec/collection-spec.md +++ b/collection-spec/collection-spec.md @@ -270,15 +270,16 @@ It is recommended to use the official The following table explains places where custom STAC `rel` types are used for Collections. This is done where there is not a clear official option, or where STAC uses an official type but adds additional meaning for the STAC context. -| Type | Description | -| ------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -| self | STRONGLY RECOMMENDED. *Absolute* URL to the location that the Collection file can be found online, if available. This is particularly useful when in a download package that includes metadata, so that the downstream user can know where the data has come from. | -| root | URL to the root STAC entity (Catalog or Collection). Collections should include a link to their root, even if it's the root and points to itself. | -| parent | URL to the parent STAC entity (Catalog or Collection). Non-root Collections should include a link to their parent. | -| child | URL to a child STAC entity (Catalog or Collection). | -| item | URL to a STAC Item. All Items linked from a Collection MUST refer back to its Collection with the [`collection` relation type](../item-spec/item-spec.md#relation-types). | -| license | The license URL(s) for the Item SHOULD be specified if the `license` field is **not** a SPDX license identifier. | -| derived_from | URL to a STAC Collection that was used as input data in the creation of this Collection. See the note in [STAC Item](../item-spec/item-spec.md#derived_from) for more info. | +| Type | Description | +| ------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | +| self | STRONGLY RECOMMENDED. *Absolute* URL to the location that the Collection file can be found online, if available. This is particularly useful when in a download package that includes metadata, so that the downstream user can know where the data has come from. | +| root | URL to the root STAC entity (Catalog or Collection). Collections should include a link to their root, even if it's the root and points to itself. | +| parent | URL to the parent STAC entity (Catalog or Collection). Non-root Collections should include a link to their parent. | +| collection | URL to a parent Collection. *Absolute* URLs should be used whenever possible. The referenced Collection is STRONGLY RECOMMENDED to implement the same STAC version as the Collection. A link with this `rel` type is *required* if the `collection` field in properties is present. | +| child | URL to a child STAC entity (Catalog or Collection). | +| item | URL to a STAC Item. All Items linked from a Collection MUST refer back to its Collection with the [`collection` relation type](../item-spec/item-spec.md#relation-types). | +| license | The license URL(s) for the Item SHOULD be specified if the `license` field is **not** a SPDX license identifier. | +| derived_from | URL to a STAC Collection that was used as input data in the creation of this Collection. See the note in [STAC Item](../item-spec/item-spec.md#derived_from) for more info. | A more complete list of possible `rel` types and their meaning in STAC can be found in the [Using Relation Types](../best-practices.md#using-relation-types) best practice.