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Re: Value-based comparison and GML

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Thu, 24 Nov 2011 09:43:40 +0000
Message-ID: <4ECE11CC.8040508@epimorphics.com>
To: public-rdf-wg@w3.org


On 23/11/11 22:44, Richard Cyganiak wrote:
> Hi Andy,
>
> Thanks for the comments. I have one question below where I didn't
> understand your response.
>
> On 21 Nov 2011, at 22:37, Andy Seaborne wrote:
>> Q0: should XML Literals be optional?
>>
>> Yes
>>
>> (I'm pulling this out as I see it not as a consequence of Q2 but as
>> a design requirement)
>
> Ok, noted.
>
>>> Q1. Should the specs define a way to compare XML literals based
>>> on value?
>>>
>>> In other words, in the same way that integers 7 and 007 have the
>>> same  value, should<foo/>  and<foo></foo>  be defined as having
>>> the same value?
>>
>> -1
>>
>> A user has worked with GML literals, which some times have 2 or
>> more attributes.  The sorting requirement of
>> exclusive-canonicalization was a surprise to them and meant that
>> putting output from a geospatial database into RDF using
>> ^^rdf:XMLLiteral didn't work.
>
> This seems like an argument that responds to Q6 (Should
> authors/generators of Turtle documents be expected to produce
> canonicalized rdf:XMLLiterals?) and not to Q1. From the GML case that
> you describe, I don't follow how you arrive at opposing
> infoset/C14N-based comparison for XML literals.

GML Literals, taken from a GIS system, don't come out in canonicalized 
form.  There is no control over the production of the GML strings.  They 
come out of an existing system; adding an XML parser into the process at 
this step (canonicalization) is heavy.

Because the equality rules are complicated and not well-known, I think 
that the spec (we aren't going to have an XMLLiteral spec as I recall) 
is tying itself in knots.

Add in HTML (more important than strict XML?) and equality is looking a 
bit arbitrary.

>> You could argue that it should not be an XML literal, but it seems
>> more reasonable to make it a derived type of XML literal (it is XML
>> after all) then the canonicalization rules would apply.
>>
>> It's a tradeoff.  I favour weaker equality for more usability.
>
> Usability, in my understanding, would be about what is a valid
> document (that is, what goes into the parser), or what goes into and
> comes out of an RDF API. Comparing XML literals based on value
> shouldn't affect that.
>
> So did you respond to Q6 here, or am I misunderstanding your
> argument?

There isn't the practical possibility of controlling the production.

>
> Best, Richard

	Andy
Received on Thursday, 24 November 2011 09:44:26 GMT

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