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<http://www.w3.org/XML/Schema/>
Member, W3C SML WG<http://www.w3.org/XML/SML/>
(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.