To facilitate the management of resource contention, and to allow resources to be cached locally, all resources returned will include a version ID and a last updated date.
The version ID and last updated date are specified in the “meta” section of the resource - for example:
<Flag xmlns="http://hl7.org/fhir"> <id value="744eec7d-8951-4722-ad74-dc34e86d4e1a"/> <meta> <versionId value="25777f7d-27bc"/> <lastUpdated value="2013-02-02T12:02:47+00:00"/> <profile value="https://fhir.nhs.uk/STU3/StructureDefinition/RARecord-Flag-1"/> </meta> <!-- Flag resource content --> </Flag>
The version ID value is specific to the version of the flag (in the above example: 25777f7d-27bc), and will change every time this specific flag resource is updated (the resource ID in the “id” field will remain the same). The version ID can be any value valid as per the id datatype, and may not be a sequential number - clients should not infer any specific meaning on the values of the ID. The lastUpdated date is the date when the resource was updated to the specified version.
Resources returned in a bundle will each have their own ID and versionID values within the resource, but in addition, where a client does a READ on an individual resource by ID, the versionID and last updated date for the resource will also be returned in an ETag and Last-Modified HTTP headers:
HTTP 200 OK Date: Sat, 09 Feb 2013 16:09:50 GMT Last-Modified: Sat, 02 Feb 2013 12:02:47 GMT ETag: W/"25777f7d-27bc" Content-type: application/json+fhir ... Resource content as above ...
ETag headers which denote resource version IDs SHALL be prefixed with W/ and enclosed in quotes, for example:
NOTE: The above does not mean that the API provides access to older versions of resources - the versionID for older versions of a resource are not made available (for example through a VREAD operation).