Re: [precis] I-D Action: draft-ietf-precis-7564bis-09.txt

Peter Saint-Andre <stpeter@stpeter.im> Fri, 21 July 2017 03:08 UTC

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To: William Fisher <william.w.fisher@gmail.com>
References: <150024725625.303.17137036571104960991@ietfa.amsl.com> <33f7468c-6742-7cbe-fa6f-70002c35cc62@stpeter.im> <CAHVjMKGcaC80UppnLV07A-GKKo16x5eMQ4BsKF5A2LEcdUm-CQ@mail.gmail.com>
Cc: precis@ietf.org
From: Peter Saint-Andre <stpeter@stpeter.im>
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Date: Thu, 20 Jul 2017 21:08:13 -0600
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Subject: Re: [precis] I-D Action: draft-ietf-precis-7564bis-09.txt
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On 7/19/17 11:30 PM, William Fisher wrote:
>> What do implementers think is a "reasonable number of iterations"? My
>> sense is that we're talking about at most 4 or 5, and usually 2 or 3.
> 
> I interpreted the word "iteration" to mean "reapplication" of the
> rules; not counting the first application. The Nickname test cases
> become stable after 2 iterations of the rules.
> 
>   output1 = precis_encode(input)
>   output2 = precis_encode(output1)      # iteration 1
>   output3 = precis_encode(output2)      # iteration 2 confirms that
> output3 == output2
> 
> I can't come up with a Nickname test case that requires more than 2
> iterations to become stable, but that doesn't mean they don't exist.

As far as I can determine based on reviewing various code points, that's
right. This _should_ be a function of the code points involved (i.e.,
how many steps a code point is from something more stable), not the profile.

> It's possible that a new PRECIS profile could be defined that has
> stability issues. IMO, if a PRECIS profile isn't stable after 3
> iterations, it's broken.

Agreed.

> The last sentence might read like this:
> 
>   Therefore, an implementation SHOULD reapply the rules
>    repeatedly until the output string is stable; if the output string
>    does not stabilize after three iterations, the
>    implementation SHOULD reject
>    the input string as invalid.
> 
> In the worst case, this means that you are calling precis_encode()
> four times for an input string.

That seems reasonable.

Peter

> 
> -Bill
> 
> 
> On Wed, Jul 19, 2017 at 6:40 PM, Peter Saint-Andre <stpeter@stpeter.im> wrote:
>> On 7/16/17 5:20 PM, internet-drafts@ietf.org wrote:
>>>
>>> A New Internet-Draft is available from the on-line Internet-Drafts directories.
>>> This draft is a work item of the Preparation and Comparison of Internationalized Strings of the IETF.
>>>
>>>         Title           : PRECIS Framework: Preparation, Enforcement, and Comparison of Internationalized Strings in Application Protocols
>>>         Authors         : Peter Saint-Andre
>>>                           Marc Blanchet
>>>       Filename        : draft-ietf-precis-7564bis-09.txt
>>
>> Our area director pointed out to me offlist that the definition of
>> "reasonable" is vague in the following text:
>>
>>    Because of the order of operations specified here, applying the rules
>>    for any given PRECIS profile is not necessarily an idempotent
>>    procedure (e.g., under certain circumstances, such as when Unicode
>>    normalization form KC is used, performing Unicode normalization after
>>    case mapping can still yield uppercase characters for certain code
>>    points).  Therefore, an implementation SHOULD apply the rules
>>    repeatedly until the output string is stable; if the output string
>>    does not stabilize within a reasonable number of iterations, the
>>    implementation SHOULD terminate application of the rules and reject
>>    the input string as invalid.