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Re: Various issues with using CURIEs in OWL

From: Shane McCarron <shane@aptest.com>
Date: Thu, 09 Apr 2009 18:15:45 -0500
Message-ID: <49DE81A1.8080604@aptest.com>
To: Bijan Parsia <bparsia@cs.manchester.ac.uk>
CC: www-html-editor@w3.org, W3C OWL Chairs <team-owl-chairs@w3.org>
My (personal) comments inline:

Bijan Parsia wrote:
> The OWL Working Group had intended to delegate our URI abbreviation 
> mechanisms both for in-spec and in-concrete-syntax use. OWL has a 
> number of different concrete serializations (including 2 XML based and 
> 2 non-XML based), all of which use (or I would like to use) CURIEs.
> Unfortunately, while trying to use the CURIE spec, I (and others) have 
> found that the current CURIE spec does not meet the WG needs even 
> putting aside concerns about the ultimate disposition of the document:
> 1) For non-XML host language: The CURIE spec provides no mechanism 
> (although it provides permission) for excluding characters from the 
> syntax of the local part of CURIEs. This means that in host languages 
> which use symbols like ")" or "[" as part of their syntax, we run into 
> parsing ambiguities. Note that safe CURIES do not solve this problem 
> as the safe CURIE delimiters are common host language delimiters.
> PROPOSED FIX: Ideally, there would be a "mimimalistic" CURIE profile, 
> ideally something like SPARQL's abbreviation mechanism. Even QNames 
> would be fine (though we'd recommend the spec point out that to cover 
> all URIs there should be a non-abbreviated form).
The lexical form of a CURIE is an optional prefix, separator, and a 
reference.  Are you saying that the characters permitted in prefix 
(NCName) or reference (irelative-ref as defined in the IRI spec) are too 
rich a set of characters?  And that in your use you needed to make this 
collection of characters less rich?  If so, I agree that this is 
permitted by the specification. 
> Note that *permission* to make a subset isn't all that helpful. I 
> mean, then we're just doing our own thing, yeah?
Not really - it means you are defining a subset or profile of a common 
mechanism, and that a CURIE expressed in that subset would be 
semantically still a CURIE.  One reason for using a common datatype is 
that it helps with comprehension.
> EDITORIAL NOTE: Many of us found the organization of the spec, and 
> especially of the normative parts, very confusing. See:
> <http://www.w3.org/mid/943ED7DE-FBC9-4110-B17B-AF9F8043A0A1@cs.man.ac.uk>
> I suggest that "Usage" and "Examples" be consolidated, and that there 
> are two normative sections, "Syntax" and "Incorporating CURIEs into 
> Host Languages" which contain the respective constraints. The second 
> section could usefully be broken down into "XML host languages" and 
> "Non-XML host languages".
Thanks for this.  We are already done with CR more or less, but I will 
see what I can do.
> 2) For XML host languages: The requirement to support the XML 
> namespace based prefix declaration mechanism, even when an alternative 
> mechanism is supplied, is simply a non-starter. Many in the XML world 
> are hostile to the namespace based overloaded (even for proper QNames! 
> see RELAX NG and Schematron). But being forced to support *two* 
> mechanisms, especially when one of them isn't desired, is 
> unnecessarily restrictive and leads to the second mechanism not being 
> used:
>    <http://www.w3.org/mid/29397.1237034265@ubehebe>
The XHTML 2 Working Group has already agreed to remove this 
restriction.  In fact, what we agreed was that it was the host 
language's responsibility to define its prefix mapping mechanim(s).
> 3) For XML host languages: There's no reason not to have a standard 
> prefix declaration mechanism in the XML namespace. What value is there 
> in letting XML host languages coin a bunch of different ones?
> For example, <xml:Prefix name="" IRI=""/> is (basically) the syntax 
> we're adopting, except with Prefix in the OWL namespace.
Perhaps.  The XHTML 2 Working Group does not have authority to mess in 
the xml space.  I am sure the group will discuss your suggestion.
> 4) Processing: In some languages, multiple declarations of a prefix 
> have an overriding behavior. In OWL we chose to make that a syntax 
> error. The CURIE spec should make clear the processing model.
We believe the processing model is completely host-language specific.  
The concept of a CURIE, that is an abbreviation that maps to an IRI, is 
general.  The expression of that concept in a host language is 
necessarily going to be related to that host language.  For example, 
were you to use CURIEs in HTML you would not want to use some "xml" 
mechanism to map a prefix.
> To sum, I, personally, don't think the CURIE spec helps either with 
> implementation interop or with spec factoring, though I think it could 
> be made to. Thus, in its current form, there's no point in citing it 
> and, thus, no real point in it being a recommendation. The minimal 
> necessary changes from my pov are:
>     A) A proper XML mechanism with no requirement to suport xmlns
>     B) Sensible profiles (I suggest, QName/RDF, SPARQL, and ALL)
>     C) A processing model
> C could maybe be dropped. A is totally required. I just won't adhere, 
> or recommend anyone adhere, to the requirement to use xmlns. It's a 
> nonstarter. Thus I won't use or recommend people use the CURIE spec 
> (in its current form) for XML based host languages.
I think we have already addressed this requirement.  Thanks for 
reinforcing it though.
> I won't use or recommend citing the CURIE spec without B for non-XML 
> host languages. If you are happy with this being "using curies" then 
> ok :)
> Hope this helps.
I think it did!  I really appreciate your taking the time to send this.  
The working group will get you a formal response in due course.
> Cheers,
> Bijan.

Shane P. McCarron                          Phone: +1 763 786-8160 x120
Managing Director                            Fax: +1 763 786-8180
ApTest Minnesota                            Inet: shane@aptest.com
Received on Thursday, 9 April 2009 23:16:31 UTC

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