Identifier numbers

A registry needs to hand out labels that are unique, permanent and uncontroversial. Names fail on all three: they get argued over, they need translating, and they go stale when the thing they name is revised. Numbers fail on none of them. The next document is simply the next number, and nobody has to agree what it should be called.

The cost is that the label carries no information. You cannot tell from the value that RFC 793 specifies TCP, that ISO 9001 is about quality management, or that the Intel 4004 was the first commercially available microprocessor. Every one of those has to be looked up — which is precisely what a registry is for.

The registries in this hub are independent of one another and use incompatible schemes. The IETF numbers its documents in one continuous sequence stretching back to 1969, so a low RFC number means an old document and nothing else. ISO and IECissue catalogue numbers that group loosely by subject but are never reused, so a withdrawn standard's number stays withdrawn. IANA assigns port numbers from a range where anything below 1024 requires privilege to bind — one of the few cases where the value carries a real consequence.

Outside computing the pattern repeats. Astronomical catalogues number objects in the order they were observed, minor planets in the order their orbits were confirmed, and the UN dangerous goods list assigns a number to a substance so a responder can identify a tanker without asking the driver. Manufacturers number parts, and a few of those numbers — 555, 741, 747 — became the everyday name of the thing itself.

A handful of identifiers are recognised by people who have never heard of the body that issued them. 404is the clearest case: it appears on posters and in conversation as a word meaning "missing", entirely detached from the status code registry that defines it. 747 and 911 are model numbers used as the names of the aircraft and the car.

The reverse also happens. RFC 911 documents a 1984 gateway protocol and shares its value with the American emergency number by pure coincidence — two registries reaching the same figure with no connection whatsoever. That is the ordinary situation, and it is why an identifier always needs its registry named alongside it.

Every identifier record here names the body that issued it and the period it has been in force, because those are the only facts that make the number mean anything. Where a value is used by more than one registry — and with over a hundred identifiers in the catalogue that is common — each meaning is recorded separately on the same number's profile rather than merged. 718 is a Porsche and a nickel superalloy; 1149 is an April Fools' RFC about carrier pigeons and the JTAG boundary scan standard. Neither pairing implies anything.