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Timestamps Extension Specification

  • Title: Timestamps
  • Identifier: timestamps
  • Field Name Prefix: -
  • Scope: Item
  • Extension Maturity Classification: Proposal

This document explains the fields of the Timestamps Extension to a STAC Item. Allows to specify numerous timestamps for assets and metadata in addition to created, updated and datetime (incl. start and end).

Item fields

Field Name Type Description
published string Date and time the corresponding data (see below) was published the first time.
expires string Date and time the corresponding data (see below) expires (is not valid any longer).
unpublished string Date and time the corresponding data (see below) was unpublished.

At least one of the fields must be specified.

All timestamps MUST be formatted according to RFC 3339, section 5.6.

The timestamps have different meaning depending on where they are used. If those fields are available in the Item properties, it's referencing to the timestamps valid for of the metadata. Having those fields in the Item assets refers to the timestamps valid for the actual data linked to in the Asset Object.

Lifecycle

An overview over the lifecycle of data and their corresponding timestamps:

  1. Data capture, start: start_datetime
  2. Data capture, often center: datetime
  3. Data capture, end: end_datetime
  4. Data first modified (stored): created
  5. Data last modified: updated
  6. Data first published: published
  7. Data last published: N/A
  8. Data valid until: expires
  9. Data removed / unpublished: unpublished

Implementations

  • openEO implements the expires field.

Outlook

Once these fields get broadly adopted, it is planned to move them to Common Metadata and place them together with created and updated. As this extension doesn't have a prefix, it doesn't lead to any breaking changes and the thus it is only a structural change for the specification.

This fields - together with created and updated - also seem relevant for STAC Collections and may be adopted there, too, for both metadata and collection-level assets.