ISO 2711 is a standard superseded by ISO 8601. Identification of days by ordinal dates was originally defined in ISO 2711. It was issued in 1973.
References
ISO 2711 Wikipedia(Text) CC BY-SA
ISO 2711 is a standard superseded by ISO 8601. Identification of days by ordinal dates was originally defined in ISO 2711. It was issued in 1973.