Re: Arabic letters and Extended Arabic letters

From: John Clews (
Date: Thu Sep 18 1997 - 07:05:18 EDT

Dear Hazem

In message <> via
you wrote:...

> I don't know the criteria followed to order the letters in Unicode.

Unicode and ISO/IEC 10646 do not have sorting within its scope.
A separate standard (ISO/IEC 14651) now under development by the
ISO/IEC working group ISO/IEC/JTC1/SC22/WG20 will cover the
multilingual sorting sequence of characters in Unicode and
ISO/IEC 10646.

Coding, sorting, and fonts are independent issues in computer
standardization, and are handled by separate standards, although many
of the standardizers are active in two or more of the fields above,
which enables continuity and consistency.

> For example why are the extended Arabic letters not imbedded within the
> Arabic letters. At least Urdu and Persian languages are still living
> languages using these letters.

Using existing ISO character set standards as a starting point was
one way that ISO/IEC 10646 (and Unicode, unified with it as far as
codepoints are concerned) was one reason for the current layout.

Thus where there was a predominant language which used a subset of
all possible characters in a given script, this affected the choice
of characters (and enabled easier backwards compatibility for data in
the predominant language). "Additional" characters were just added on
afterwards. Computer systems can and generally do cope well with this.

Comparing the Cyrillic and Arabic tables in ISO/IEC 10646 (and also
in Unicode) with their "equivalents" in ISO/IEC 8859-5 and ISO/IEC
8859-6 will show you what I mean.

> Another question is why is the shaping included (it's even far from the
> isolated shape)? Shouldn't that be in the font page or something?

This is what font developers will do. Again, this is beyond the scope
of ISO/IEC 10646. If ISO/IEC 10646 prescibed font shapes, there would
be uproar.

There is however a character glyph model developed elsewhere within
ISO/IEC/JTC1 which provides systems developers with useful background
information in this regard.

                                   Yours sincerely

                                     John Clews

John Clews (Chair of ISO/TC46/SC2: Conversion of Written Languages)

SESAME Computer Projects, 8 Avenue Road, Harrogate, HG2 7PG, England Email:; tel: +44 (0) 1423 888 432

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