From: Asmus Freytag (firstname.lastname@example.org)
Date: Thu Jul 09 2009 - 03:34:17 CDT
What Karl describes is a real concern. But it is not that different from
many other changes in property assignments for individual characters. If
your process relies on particular property values for particular
characters, then you need to add assertions to your database update code
that trigger when you go to a new version of the Unicode Character Database.
For "empty" properties, those are easy to detect, and it is good
practice to have your script report whenever any defined property is empty.
On 7/8/2009 9:28 PM, Phillips, Addison wrote:
> What the policy guarantees is that implementations that rely on a particular property name or value being valid will not suddenly find that they specify values that are not legal property names or property values. A negative counter-example prompting this policy was the change of the script value 'Greek' to 'Greek_and_Coptic".
> This is an important guarantee, independent of whether a given property name or property value is currently in use or which set of code points (including the empty set) is assigned particular name-value pairings. Certainly implementations of UTS#18 (regular expressions) rely on it, as do such things as XML Schema 1.1.
> You are right that implementations may still struggle with formerly useful property names or values now being essentially useless. But your code will still work according to the current expectations of the current version of Unicode. Other stability policies might be worth examining, but they are orthogonal to whether names or values can be respelled at a later date.
> Addison Phillips
> Globalization Architect -- Lab126
> Chair -- W3C Internationalization WG
> Internationalization is not a feature.
> It is an architecture.
>> -----Original Message-----
>> From: email@example.com [mailto:firstname.lastname@example.org]
>> On Behalf Of karl williamson
>> Sent: Wednesday, July 08, 2009 4:02 PM
>> To: email@example.com
>> Subject: Property stability policy considered harmful
>> It appears to me that the stability guarantees that a property and
>> property value alias will never be removed are worse than not
>> them. And the reason is that all code points they contain can
>> simply be
>> moved to another property (or property value) without violating the
>> letter of the policy. This has happened with
>> Script=Katakana_Or_Hiragana whose contents were all moved to Common
>> 4.1, and it appears to be happening in 5.2 with ISO_Comment. If I
>> a program that is looking for a property that has become empty, I
>> rather know about it at compilation time rather than to have it go
>> and give wrong answers (perhaps subtly so).
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