RE: [w3c sml][4665] Clarify URI equivalence in reference to RFC 3986

As I interpret "case insensitive", it means "a"=="A".  Is that how you 
mean it?
If so then I fail to see how this is simpler than "case sensitive" 
comparison.  Case-insensitive requires normalization (to one case), which 
is in direct opposition to your own first argument.  Thus, to me, it is 
confusing unless there is some other factor not yet expressed that makes 
this a tradeoff worth doing.  Requiring case normalization _might_ also 
cause burdens on implementations that choose to support encodings other 
than utf-8/16.  I am _far_ from an expert on encodings, but I do remember 
hearing about cases involving Katakana I believe where case-folding was 
quite expensive.  If this becomes a critical factor in the decision I will 
have to talk to some globalization folks.
This seems to me like it might be another floor/ceiling discussion.  3986 
clearly discusses the tradeoff between computational cost and the risk of 
concluding that two URIs identify distinct resources when they do not, 
because of incomplete normalization (I think it refers to this case as 
false negative, but the language makes my head hurt so I wrote it out). It 
seems as if we can allow simple string comparison as a floor without 
precluding more sophisticated implementations from climbing further up the 
comparison ladder.  Remember that the risk in our context of believing two 
URIs refer to different things is the risk of getting the model boundary 
wrong in the interchange case.  Interop would only be guaranteed at the 
floor of course, as usual, but it is still sufficient for interop.

Best Regards, John

Street address: 2455 South Road, Poughkeepsie, NY USA 12601
Voice: 1+845-435-9470      Fax: 1+845-432-9787



Kumar Pandit <kumarp@windows.microsoft.com> 
Sent by: public-sml-request@w3.org
09/19/2007 06:15 PM

To
Sandy Gao <sandygao@ca.ibm.com>, "public-sml@w3.org" <public-sml@w3.org>
cc
Kumar Pandit <kumarp@windows.microsoft.com>
Subject
RE: [w3c sml][4665] Clarify URI equivalence in reference to RFC 3986






I added the ‘case insensitive’ clause because, if an implementation is 
based on a file-system that uses case insensitive paths then it fits 
nicely with the current proposal. That said, I do not have a strong bias 
towards that option. I am ok with defining the comparison as case 
sensitive while keeping the rest of the definition as is.
 
It is not clear from your reply if you agree with the proposal (sans the 
case-insensitive part) or if you want to base your decision on whether the 
URI/IRI gurus agree with it first. Can you please clarify?
 
Since no one has disagreed with the proposal (except the concern about 
case-insensitive part), if you agree with the amended wording, we may 
actually be able to get this into the second draft today.
 
 
From: public-sml-request@w3.org [mailto:public-sml-request@w3.org] On 
Behalf Of Sandy Gao
Sent: Wednesday, September 19, 2007 11:11 AM
To: public-sml@w3.org
Subject: Re: [w3c sml][4665] Clarify URI equivalence in reference to RFC 
3986
 

This is a simple proposal, and being simple is normally good, but I'll 
leave this to the URI/IRI gurus to determine whether the simple solution 
is good enough to cover real-life scenarios.

One thing that worries me is the "case insensitive" part. Why? As far as I 
can tell, this doesn't match any of the steps in "6.2. Comparison Ladder" 
of RFC 3986. If we want the simplest possible solution, then we should use 
what's defined in 6.2.1 and compare strings character-by-character 
case-sensitivly. 

Thanks,
Sandy Gao
XML Technologies, IBM Canada
Editor, W3C XML Schema WG
Member, W3C SML WG
(1-905) 413-3255 T/L 969-3255



Kumar Pandit <kumarp@windows.microsoft.com> 
Sent by: public-sml-request@w3.org 
2007-09-12 11:02 PM 


To
"public-sml@w3.org" <public-sml@w3.org> 
cc
Kumar Pandit <kumarp@windows.microsoft.com> 
Subject
[w3c sml][4665] Clarify URI equivalence in reference to RFC 3986
 








Here is my proposal to resolve this issue. 
  
Proposal: 
Uri equivalence in SML-IF should be defined as case insensitive simple 
string comparison based on codepoint-by-codepoint comparison of the 
corresponding characters in the uri. 
  
Justification: 
1.        Performance: Simple string comparison provides highest 
performance. Although it is true that two aliases of the same uri may not 
compare as equal without normalization, the problem does not exist in the 
specific context of an SML-IF producer. This is because, when a producer 
is writing out an SML-IF document, it can apply normalizations (if 
necessary) such that a given uri always appears in the same way. This 
allows consumers to perform fast string comparison without needing to 
perform any type of normalization. 

RFC 3986 section 2 (Comparison Ladder) describes many different forms of 
normalizations 
(syntax-based/case/percent-encoding/path-segment/scheme-based/protocol-based). 
If we want a consumer to perform normalizations, we not only make a 
consumer less efficient but also need to add very specific normalization 
step definitions in the SML-IF spec. On the other hand, if we leave the 
burden of normalization to the producer, we can keep the SML-IF spec much 
simpler and allow consumers to be more efficient. This way the spec does 
not need to talk about any specific comparison ladder step(s) to be 
performed by a producer. The producer is free to apply any (or none) 
normalization steps as long as it knows it will write a given uri in the 
same format. 
2.        Precise definition: RFC 3986 section 6.2.1 (Simple String 
Comparison) discusses issues involved in performing a string comparison 
but does not provide a precise definition of how the comparison must be 
performed. In other words, it leaves some room for interpretation. We 
should avoid this by presenting an unambiguous definition based on that 
discussion.