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.