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Re: ISSUE: Using @id to set subject in RDFa (ISSUE-121)

From: Ivan Herman <ivan@w3.org>
Date: Sun, 20 Nov 2011 09:41:54 +0100
Cc: RDFa WG <public-rdfa-wg@w3.org>
Message-Id: <2AB43094-3365-4E02-AB62-52C52A7784F5@w3.org>
To: Sebastian Heath <sebastian.heath@gmail.com>

(This is my personal answer, and not an official answer from the group)

this is not an error report on an existing feature; instead, it is a request for a new feature. As such, my first question is: is there a convincing evidence that this functionality is needed by the community?

In my personal experience as a user, but also getting feedbacks from other users, I do not see this as a major feature request from the community. At least in my case, almost all (if not all, I have not checked) usage of @about uses a URI that does _not_ bind to an @id value (whether that URI uses a fragment id or not). The reason is that when encoding information in RDF on some specific subject, that subject's URI is usually an 'abstract' URI (URI of a person, a paper, a presentation, etc) which is not directly represented in the HTML source via an element id. An @id may be used, though, as part of the object of a triple, ie, via @href or @resource (bound to predicates like 'described by', or similar).

That is at least my experience. Based on that I am not in favour adding yet another feature to RDFa which is already quite rich (other would say 'complicated') in features...

Sorry about that...



On Nov 19, 2011, at 19:02 , Sebastian Heath wrote:

> Currently, RDFa processors do not take account of @id attributes in
> host-languages. In particular, in (x)html the @id attribute is
> ignored. In (x)html, this creates unnecessary complication in which
> the value in @id needs to be prefixed by '#' and put in an @about
> attribute in order to make semantic markup visible to both html agents
> and rdfa processors.
> Example:
> <p id="item1" typeof="ex:item" about="#item1">
>   <span property="item_name">An interesting item (1)</span>
> </p>
> I suggest that a combination of @typeof and @id cause the subject to
> be set to the fully qualified URL implied by the value @id, according
> to normal URL processing rules defined for HTML and related languages.
> Given a document http://example.org/document1 with appropriate
> @vocab/@prefix definitions, this would lead to the markup
>  <p id="item1" typeof="ex:item">
>   <span property="rdfs:label">An interesting item (1)</span>
> </p>
> producing the triples
> <http://example.org/document1#item1> rdf:type <http://example.org/ns/item> .
> <http://example.org/document1#item1> rdfs:label "An interesting item (1)" .
> The main advantage is the simplicity of using a single construct to
> make semantic data visible to both browsers, DOM aware languages such
> as javascript, and to RDFa processors.
> The restriction that the subject is only set when there is also a
> @typeof will reduce the number of so-called 'junk' triples. But I note
> that RDFa accepts the generation of such triples in other situations
> such as link elements invoking style sheets using @rel.
> It may be that this functionality is best defined for particular host
> languages and not in the RDFa 1.1 core.
> Sebastian Heath.

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Sunday, 20 November 2011 08:39:06 UTC

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