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Re: Hash URIs and RDFa documents

From: Niklas Lindström <lindstream@gmail.com>
Date: Tue, 2 Feb 2010 12:59:02 +0100
Message-ID: <cf8107641002020359j4922ff98r3b96d973c54d3bb2@mail.gmail.com>
To: Mark Birbeck <mark.birbeck@webbackplane.com>
Cc: Michael Hausenblas <michael.hausenblas@deri.org>, Stephane Corlosquet <scorlosquet@gmail.com>, RDFa TF list <public-rdf-in-xhtml-tf@w3.org>, Dan Brickley <danbri@danbri.org>
Hi!

I have been thinking the following regarding fragment identifiers.
Given an *information* resource (IR):

    http://example.org/about

Say it has the following representations:

    http://example.org/about.html
    http://example.org/about.n3

These are distinct resources.

When requesting <http://example.org/about> (an IR) with HTTP using
content negotiation (here asking for "text/html") allows the server to
send a 200 OK upon request, with the body being from
<http://example.org/about.html> (given in Content-Location).

(This is different from conneg on non-IR:s, which require 303:ing.)

I then stipulate that these two are owl:differentFrom each other (not
necessarily, but quite possibly):

    http://example.org/about#me
    http://example.org/about.html#me

The first identifies a non-IR, i.e. *me* (because I define it as that,
as (fictive) owner of example.org). The other, perhaps an element in
the html (not the bytes, but the DOM? this quickly gets slippery).

The HTTP + HTML (web browser) mechanics makes it work for me to
request <http://example.org/about#me>, receiving the html according to
above without any "change in the url bar" (i.e. "browser mechanics"),
and thus the browser view jumps to the element referenced by the
fragment identifier (the id alone, from the URI having been
*string-parsed* by the browser). But that is not the element's URI. It
*could* be, possibly, <http://example.org/about.html#me>. Those
semantics (or lack thereof) are reasonably under the provenance of the
html spec authors.

(I'm not really claiming anything about what
<http://example.org/about.html#me> identifies. I think that, even with
@id being present in the document, it's not actually defined. But for
this reason I think it's advisable to avoid using them, at least as
URI:s for non-IR:s.)

I think <http://www.w3.org/TR/cooluris/> support these claims, but I
could have mixed things up here.

What do you say?

(If these claims aren't just nonsense, getting the triples right in
RDFa for a document carrying triples about both </about> and
</about.html> (and fragments based on them) is an interesting next
exercise..)

Best regards,
Niklas



On Tue, Feb 2, 2010 at 11:13 AM, Mark Birbeck
<mark.birbeck@webbackplane.com> wrote:
> Hi Michael,
>
> I disagree with the point made in the email you refer to, from Richard.
>
> Only one triple is generated in your sample, so nowhere do we have an
> indication that #me is both a person and an HTML element in a
> document.
>
> My point is that it would be good practice to keep these things apart,
> but I think it's going too far to say that we create some kind of
> contradiction if we don't.
>
> Regards,
>
> Mark
>
>
>
> On Tue, Feb 2, 2010 at 8:38 AM, Michael Hausenblas
> <michael.hausenblas@deri.org> wrote:
>> Stephane,
>>
>> I by and large agree with Mark, however ...
>>
>>> Whilst it doesn't hurt to have an @id though, my preference would be not to.
>>
>> Hm. Not so sure about this one. Let's look at the following example,
>> namespace declarations assumed to be done already, and the base URI is
>> "http://sw-app.org/"
>>
>> 1: <div about="#me" typeof="foaf:Person">
>> 2:  <a rel="foaf:homepage" href="http://sw-app.org/about.html">my
>> homepage</a>
>> 3: </div>
>> 4: <div id="me">
>> 5:  yada yada
>> 6: </div>
>>
>> What I am saying here is that the *part of the document (4-6)*, identified
>> by "http://sw-app.org/#me, is of type foaf:Person. Richard explained it much
>> more elegant a while ago [1]. I don't think this is what we want to express.
>>
>> In any case, I'm gonna take this discussion into account for updates on [2].
>>
>> Cheers,
>>      Michael
>>
>> [1] http://lists.w3.org/Archives/Public/semantic-web/2007Dec/0157.html
>> [2] http://ld2sd.deri.org/lod-ng-tutorial/#checklist-fragid
>>
>> --
>> Dr. Michael Hausenblas
>> LiDRC - Linked Data Research Centre
>> DERI - Digital Enterprise Research Institute
>> NUIG - National University of Ireland, Galway
>> Ireland, Europe
>> Tel. +353 91 495730
>> http://linkeddata.deri.ie/
>> http://sw-app.org/about.html
>>
>>
>>
>>> From: Mark Birbeck <mark.birbeck@webbackplane.com>
>>> Date: Mon, 1 Feb 2010 22:55:12 +0000
>>> To: Stephane Corlosquet <scorlosquet@gmail.com>
>>> Cc: RDFa TF list <public-rdf-in-xhtml-tf@w3.org>, Dan Brickley
>>> <danbri@danbri.org>
>>> Subject: Re: Hash URIs and RDFa documents
>>> Resent-From: RDFa TF list <public-rdf-in-xhtml-tf@w3.org>
>>> Resent-Date: Mon, 01 Feb 2010 22:56:50 +0000
>>>
>>> Hi Stéphane,
>>>
>>> As you imply, there is actually no need for an @id value. For some
>>> reason many examples that people have created in the past have tried
>>> to align @about and @id, but it really isn't necessary.
>>>
>>> Whilst it doesn't hurt to have an @id though, my preference would be not to.
>>>
>>> As things stand today it's unlikely that there would be a confusion,
>>> but I don't know if you are familiar with @role (another W3C standard
>>> which myself, Shane and Steven have been involved in), but with that
>>> you really are making statements about an HTML element. I'm hoping
>>> that the RDFa/@role story is properly fleshed out at some point, so I
>>> think it would be good to try to keep the boundaries clear, ready for
>>> this.
>>>
>>> So I'd vote for your second option. :)
>>>
>>> Regards,
>>>
>>> Mark
>>>
>>> --
>>> Mark Birbeck, webBackplane
>>>
>>> mark.birbeck@webBackplane.com
>>>
>>> http://webBackplane.com/mark-birbeck
>>>
>>> webBackplane is a trading name of Backplane Ltd. (company number
>>> 05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
>>> London, EC2A 4RR)
>>>
>>>
>>>
>>> On Mon, Feb 1, 2010 at 9:45 PM, Stephane Corlosquet
>>> <scorlosquet@gmail.com> wrote:
>>>> Hi,
>>>>
>>>> Imagine an RDFa document describing a person. The foaf:Document URI is <>
>>>> and the foaf:Person URI is <#person> because you want to be able to
>>>> distinguish between the two; also foaf:Document and foaf:Person are
>>>> disjoint.
>>>>
>>>> <>        a foaf:Document .
>>>> <#person> a foaf:Person .
>>>> <> foaf:primaryTopic <#person> .
>>>>
>>>> If the document is describing an online account, it might have
>>>> <>        a sioc:User .
>>>> <#person> foaf:account <>.
>>>>
>>>> My concern is about the #person fragment with regard to the HTML document.
>>>> If the page is only about one person, there might not be a tag with
>>>> id="person" in the page. Is this a problem? Should I have a tag with such
>>>> id, or, on the contrary, should I avoid this as to ensure the resource being
>>>> described is not confused with the actual HTML tag contained in the page?
>>>>
>>>> cc'ing Dan since this message is related to his point #5 at
>>>> http://danbri.org/words/2010/01/14/549
>>>>
>>>> regards,
>>>> Stéphane.
>>>>
>>>
>>
>>
>
>
Received on Tuesday, 2 February 2010 11:59:56 GMT

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