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 Post subject: Compatibility Variants vs Compatibility Decomposable Charact
PostPosted: Sat Dec 15, 2012 1:07 pm 
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On page 20 of Chapter 2: General Structure, you'll find the definitions of Compatibility Variants and Compatibility Decomposable Characters. What's the difference between these two sets of characters? If they are not the same, I'd appreciate having an example of a character that is a compatibility variant but not a compatibility decomposable character or vice versa.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sat Dec 15, 2012 2:05 pm 
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One example is given right there in the text, CJK Compatibility Ideographs.

I'll let you look up their properties and compare that to the definitions so you will see for yourself why they are an example for what you are after.

Also, please note, that formal, normative definitions of terms are only found in chapter 3 of the standard (and the definition sections of some UAXs). The explanations of terms in other chapters and in the glossary are generally informal and informative and serve as an aid to the reader. In some circumstances they paraphrase, reference, elaborate or cite an existing formal definition.

The concepts behind the terms "compatibility character" and "compatibility variant" are useful in understanding the standard and its development, but they are purposefully not presented as formal definitions.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sat Dec 15, 2012 2:13 pm 
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asmus wrote:
One example is given right there in the text, CJK Compatibility Ideographs.
I just found your earlier post and now see that you are already quite familiar with this example.

You had asked in the CJK Compatibility Ideographs thread:
Kalane wrote:
Why the CJK Compatibility Ideographs are not compatibility decomposable characters ?
where you did receive a detailed answer.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sat Dec 15, 2012 3:24 pm 
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asmus wrote:
One example is given right there in the text, CJK Compatibility Ideographs.

I'll let you look up their properties and compare that to the definitions so you will see for yourself why they are an example for what you are after.

Also, please note, that formal, normative definitions of terms are only found in chapter 3 of the standard (and the definition sections of some UAXs). The explanations of terms in other chapters and in the glossary are generally informal and informative and serve as an aid to the reader. In some circumstances they paraphrase, reference, elaborate or cite an existing formal definition.

The concepts behind the terms "compatibility character" and "compatibility variant" are useful in understanding the standard and its development, but they are purposefully not presented as formal definitions.


Chapter 3 makes no reference to Compatibility Variants. Where is the formal definition of a compatibility variant character in Unicode? One thing I can't understand; the CJK Compatibility Ideographs are compatibility variants, but they are not compatibility decomposable characters. However, Arabic Presentation Forms A and B are compatibility variants and compatibility decomposable characters. Why the difference?


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sat Dec 15, 2012 4:01 pm 
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Kalane wrote:
asmus wrote:
The concepts behind the terms "compatibility character" and "compatibility variant" are useful in understanding the standard and its development, but they are purposefully not presented as formal definitions.
Chapter 3 makes no reference to Compatibility Variants. Where is the formal definition of a compatibility variant character in Unicode?
There isn't one. Which I already mentioned, see the highlighted part of my reply.

Kalane wrote:
One thing I can't understand; the CJK Compatibility Ideographs are compatibility variants, but they are not compatibility decomposable characters. However, Arabic Presentation Forms A and B are compatibility variants and compatibility decomposable characters. Why the difference?
You already asked basically the same question and did receive an answer from a knowledgeable expert. If that answer was insufficient or unclear, the best thing would be to follow this up in the other thread.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sat Dec 15, 2012 5:31 pm 
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asmus wrote:
You already asked basically the same question and did receive an answer from a knowledgeable expert. If that answer was insufficient or unclear, the best thing would be to follow this up in the other thread.

The question you refer to was about CJK ideographs and was posted at the Unihan and CJK Forum (more than a month ago) which was appropriate. This question is not, necessarily about CJK ideographs, and that's why I decided to post it here. Nevertheless, I have the impression that either, you don't want to answer my question, or you don't know how to answer it. In any case, unfortunately, I'll have to leave with empty hands. Thanks for your efforts anyway.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sat Dec 15, 2012 7:39 pm 
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You had asked
Kalane wrote:
Why the CJK Compatibility Ideographs are not compatibility decomposable characters ?
and now you are asking
Kalane wrote:
One thing I can't understand; the CJK Compatibility Ideographs are compatibility variants, but they are not compatibility decomposable characters.
I assume that you are not questioning that Compatibility Ideographs exist for compatibility or are variants of other ideographs, which is the "definition" of compatibility variant given in chapter 2. In other words, I assume that you agree that they should be Compatibility Variants.

If that's correct, it leaves the the second part of your issue. But that's the question to which user Tseng attempted to give you an answer in the other thread. All I'm suggesting is that if you need more detail, he's really the best resource.

If I'm wrong, and you are really curious about something else, perhaps it might help us if you could let us know why you are looking for an answer to this particular question.

To me, your question appears to be the same. I know, you did point to the Arabic case and asked "why the difference?" - however, I would have to answer that question in essentially pretty much the same way as user Tseng did, with a reference to why the issues of Han variants are different.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sun Dec 16, 2012 8:14 am 
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I'll repeat my question: "On page 20 of Chapter 2: General Structure, you'll find the definitions of Compatibility Variants and Compatibility Decomposable Characters. What's the difference between these two sets of characters?"

Clearly they are not the same set of characters, as the compatibility variants contains the CJK Compatibility characters which are not compatibility decomposable characters (as was explained by Tseng in my previous question). But the compatibility variants set also contains the Arabic Presentation Forms A and B which are decomposable characters.

On page 20 of Chapter 2, youl'll find the following statement:"Compatibility variants are a subset of compatibility characters".

In the next paragraph one can read "In contrast to compatibility variants there are the numerous compatibility characters, such as U+2502 box drawings light vertical, U+263A white smiling face, or U+2701 upper blade scissors, which are not variants of ordinary Unicode characters. However, it is not always possible to determine unequivocally whether a compatibility character is a variant or not."

Basically what I'm asking is: what is a compatibility variant character? If one cannot determine whether a compatibility character is a variant or not, why did Unicode waste one section of Chapter 2 trying to define this concept, and at the same time saying that the definition doesn't exist? This just sounds very odd to me.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sun Dec 16, 2012 3:15 pm 
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There is a reason why I asked you whether you had a particular purpose in following up that question. I had written:

Quote:
The concepts behind the terms "compatibility character" and "compatibility variant" are useful in understanding the standard and its development, but they are purposefully not presented as formal definitions.
These concepts are used in guiding the character encoding committees' decision on how to treat proposed characters for encoding, for example, but they are not directly required in writing an implementation that is conformant to the Standard. The only characters for which the standard requires specific treatment based on their compatibility status are the Compatibility Decomposable Characters. That's the reason why only they have a formal definition in chapter 3.

Chapter 2 is concerned with explaining, among other issues, how the Unicode Standard is organized (and, where possible, why it was organized that way), and that necessitates a discussion of the "Compatibility Area" on the BMP and certain blocks where the word "Compatibility" shows up in the name.

The distinction between Compatibility Variant vs. ordinary Compatibility Characters is not one that's driven by data tables nor can it be done algorithmically. It is, however, a distinction that can be arrived at by people (such as character encoding committees) when evaluating characters.

Compatibility may be the motivation to encode a character, but only Compatibility Variants need to be considered for possible Decomposition. (Whether to actually provide that decomposition is a judgement call, you won't find an algorithm for it anywhere).

There are many things about characters that cannot be determined unequivocally in every single case. There are even certain cases where the basic question of whether something should be a character (or a glyph, or something else) cannot be resolved in a way that leaves no doubt. Different groups of people can come to different conclusion in such cases, but when it comes to creating a standard, only the formal decision of the character encoding committee to go one way or another counts in the end.

The purpose of some of the text in chapter 2 is to tell the reader what considerations went on in creating the standard, it is not intended as an algorithmic description that would allow a new group of people to come to all the same decisions as are embodied in the current content of the standard.

You may have expected something of the latter, but it's not what the text is intended for.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sun Dec 16, 2012 6:02 pm 
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From what you said and from what is written in Chapter 2, would it be reasonable to say that:
    1. Compatibility variants = Compatibility Characters - Set of characters like U+2502 BOX DRAWINGS LIGHT VERTICAL, U+263A WHITE SMILING FACE, or U+2701 UPPER BLADE SCISSORS, which are not variants of ordinary Unicode characters (*)
    2. Compatibility variants = CJK Compatibility Ideographs + CJK Radicals Supplement + Compatibility Decomposable characters

(*) Unicode doesn't define a list for this set of characters.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Sun Dec 16, 2012 11:00 pm 
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Kalane wrote:
From what you said and from what is written in Chapter 2, would it be reasonable to say that:
    1. Compatibility variants = Compatibility Characters (*) - Set of characters like U+2502 BOX DRAWINGS LIGHT VERTICAL, U+263A WHITE SMILING FACE, or U+2701 UPPER BLADE SCISSORS, which are not variants of ordinary Unicode characters (*)
    2. Compatibility variants = CJK Compatibility Ideographs + CJK Radicals Supplement + Compatibility Decomposable characters + Any other variants not given a Decomposition(*)

(*) Unicode doesn't define a list for this set of characters.

Almost. I fixed it for you in blue.

Even if the list of other Compatibility Variants not given a Decomposition may be limited to the CJK characters today, and as there are no lists, it's hard to be sure, there's no guarantee that there won't be future characters added that fit those characteristics. So, you need to add the unspecified set of characters into expression (2) in your summary to make it come out.


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 Post subject: Re: Compatibility Variants vs Compatibility Decomposable Cha
PostPosted: Mon Dec 17, 2012 5:49 am 
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Thanks


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