- From: Steve Harris <steve.harris@garlik.com>
- Date: Thu, 17 May 2012 18:54:05 +0100
- To: Ivan Herman <ivan@w3.org>
- Cc: Richard Cyganiak <richard@cyganiak.de>, Guus Schreiber <guus.schreiber@vu.nl>, RDF WG <public-rdf-wg@w3.org>
On 2012-05-17, at 17:32, Ivan Herman wrote:
>
> On May 17, 2012, at 17:48 , Steve Harris wrote:
>
>>
>> I (occasionally) have to explain out tech stack to new developers coming in, it's not getting any easier.
>>
>> I can imagine struggling to explain why:
>>
>> <x> <p> '''<p class="foo" id="bar">baz'''^^xsd:HTMLLiteral .
>> <y> <p> "<p id='bar' class='foo'>baz</p>"^^xsd:HTMLLiteral .
>>
>> SELECT *
>> WHERE {
>> ?s <p> ?o .
>> FILTER(?o = "<p id='bar' class='foo'>baz</p>"^^xsd:HTMLLiteral)
>> }
>>
>> returned two results.
>>
>
> What would your developer expect with
>
> <x> <p> '''0123'''^^xsd:integer .
> <x> <p> "123"^^xsd:integer .
>
> SELECT * WHERE { ?s <p> ?o . FILTER( ?o = "123"^^xsd:integer ) }
>
> I would certainly expect two results, because I typed the literal. I would actually be surprised if the HTML version did not returned two results!
Well, that very much depends on the language.
In C-like languages 0123 == 123 is false of course.
123.0 is a different matter, I think the majority of programmers would expect 123 == 123.0 to be true.
So, it obviously depends on how you view "<p id='bar' class='foo'>baz</p>"^^xsd:HTMLLiteral, and HTML fragments in general.
http://stackoverflow.com/questions/3760991/are-there-any-tools-that-can-compare-html-documents-by-dom-structure suggests that even in javascript it's not common, or expected.
I can't think of many languages I'm familiar with where comparing the two DOM structures you'd get from parsing those two strings would return true, using the built in =. You have to call a method to serialise it to a normalised string, and compare the strings.
None of this suggests that SPARQL/RDF shouldn't go it's own way and do implicit normalisation, but there should be a reason to do it, to counteract the surprise factor.
- Steve
--
Steve Harris, CTO
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Received on Thursday, 17 May 2012 17:54:38 UTC