From the schema
IATI identifier This element contains the official IATI identifier for an entity (activity or organisation). It must appear only once in the XML file, and is guaranteed unique across all entities of the same type (there will never be two organisations or activities with the same IATI identifier).
Compliance1 compliance test(s) for /iati-identifier
- iati-identifier starts with the reporting-organisation ref
- iati-identifier has no leading or trailing whitespace
This is a globally unique identifier for this activity.
This is a concatenation of the unique organisation identifier (for the reporting organisation) and the organisation's activity identifier.
The example below is for an Oxfam (identified by GB-CHC-202918) activity, with their internal unique ref. of HECA91