logical order (and Thai)

From: Samphan Raruenrom (samphan@thai.com)
Date: Sat Jul 27 2002 - 11:03:22 EDT

Kenneth Whistler wrote:
> Ummm. Logical order, visual order, aural order, phonemic order,
> linear order... We are in danger of losing track of the ground we
> stand on.

Totally agree.

> Logical order versus visual order, in the Unicode Standard,
> refers to the relationship between backing store order and
> display order. The main issue is for bidirectional text.

Fortunately, this is put clear enough in the Unicode book,

> There is a separate issue which has to do with alternative
> models of Brahmi-derived scripts.
> The "Indic model" ...
> The "Thai model" ...
> Note, however, that *both* of these models inherently imply non-linear
> mappings at some level. In the Indic model, the mapping from
> phonology to backing store is straightforward, but the mapping
> from backing store to display (i.e., the "rendering") will
> have local direction reversals and/or 1-2 character-to-glyph
> mappings, in the case of reordrant or surroundrant vowels.
> The Thai model displaces the mapping complexity to the
> mapping from phonology to backing store, while simplifying the
> rendering.

But this is not. It would be easier to avoid these confusions if
the above description about "non-linear mapping" of Brahmi-derived
scripts was written clearly in Chapter 2 of the book in the
section about logical order.

> Given this picture, it should now be easier to see why Thai
> rendering is easier than Devanagari, but Thai sorting
> (which runs afoul of the mismatch between phonology and
> backing store order) in more problematical. It is simply
> a tradeoff of which level of processing gets the complexity.

Does this mean that there's nothing illogical or less-prefered
with the Thai model?
If so, please also consider the following question (a little bit

-------- Original Message --------
Subject: Logical_Order_Exception actually means Phonetic_Order_Exception ?
Date: Sat, 01 Jun 2002 12:00:09 +0700
From: Samphan Raruenrom <samphan@thai.com>
Organization: NECTEC
To: Unicode Public List <unicode@unicode.org>
CC: Thai IT Standards Newsgroup
<th.pubnet.it-stds@thaigate.r.nii.ac.jp>, Virach Sornlertlamvanich
<virach@nectec.or.th>, Trin Tansetthi <trin@mozart.inet.co.th>,
Suwit Srivilairith <suwits@th.ibm.com>

It's said (below) that ALL scripts in Unicode are stored in 'logical
order'. And for the most part, logical order corresponds to 'phonetic
order'. And the only exceptions are Thai and Lao.
Do you think that Logical_Order_Exception should actually be called

8<- References --------------------------------------------------->8
The definition of this newly introduced property in Unicode 3.2 :-
**** http://www.unicode.org/unicode/reports/tr28/#database

There are a small number of characters (in the Thai and Lao scripts)
that do not use logical order. These characters require special
handling in most processing.

The difinition of Logical Order :-
**** The Unicode Standard 3.0 : Section 2.2 Unicode Design Principles

Logical Order:
For "ALL" scripts, Unicode text is stored in 'logical order' in the
memory representation, roughly corresponing to the order in which
text is typed in via the keyboard.
For the most part, logical order corresponds to 'phonetic order'.
The only current exceptions are the Thai and Lao scripts, which
employ visual ordering; in these two scripts, users traditionnally
type in visual order rather than phonetic order.

The followings are the only Logical_Order_Excention in Unicode 3.2 :-

0E40..0E44 ; Logical_Order_Exception # Lo [5] THAI CHARACTER
0EC0..0EC4 ; Logical_Order_Exception # Lo [5] LAO VOWEL
                SIGN E .. LAO VOWEL SIGN AI

Feel free to forward or quote to any individual or public.

Samphan Raruenrom Information Research and Development Division, National Electronics and Computer Technology Center, Thailand. http://www.nectec.or.th/home/index.html

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