Re: UCS-4 as a conformant form of Uniocde

From: Kenneth Whistler (
Date: Mon Nov 09 1998 - 15:15:53 EST

Ed Hart asks:

> I have had the very distinct impression that Unicode had a preference for
> 16-bit encoding to the exclusion of the 4-octet UCS-4 form of ISO/IEC
> 10646-1:1993. I verified that UCS-4 appears to be excluded from the
> conformance clause of Unicode 2.0. However, what if I chose to implement
> the UCS-4 form of 10646 and implemented everything else but this in
> conformance to the Unicode conformance statements (character properties,
> bi-di, etc.), and my implementation was able to exchange data in
> UCS-2/UTF-16 and the UCS-4 forms? Is this implementation conformant to
> Unicode 2.0? I interpret that this implementation is not conformant to
> Unicode 2.0.

If your implementation exchanges data in UTF-16, then it is conformant
to the Unicode Standard Version 2.0 (and the fact that it uses 32-bits
internally is irrelevant).

If you implementation exchanges data in UCS-4, it may be conformant to
10646-1, but it is not conformant to the Unicode Standard Version 2.0.
(At least this interchange format is not -- an application may choose to
use multiple interchange formats, in which case it conforms to the
multiple standards that define those formats.)
> My question is why should not the UCS-4 form be included as a
> conformant form in Unicode? As we move to encoding characters into planes 1
> and beyond, I think that it makes good sense to add the UCS-4 form as
> conformant to Unicode (3.0).

As Asmus noted, how we choose to lay out tables is a separate issue from
whether the Unicode Standard moves to make UCS-4 a conformant form for
Unicode interchange.

> Ed Hart

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