Admin issue (Re: Last Call comments on RDFa Core)

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On Dec 12, 2010, at 20:26 , Harry Halpin wrote:

> Due to discussion over RDFa with some colleagues (including Kavi Goel of
> Google and Peter Mika of Yahoo! (whose own review is coming shortly and
> will hopefully give empirical evidence to some of these arguments), I
> finally sat down and read what I think is the most current RDFa document
> [4]. Evidently the deadline for review feedback has been extended for
> Shelley Powers and Peter Mika, so I attach my feedback as well.
> Overall, very good work.  I do have a number of comments to reduce the
> complexity and so encourage usability of RDFa. These comments are mine and
> represent no-one or organization besides my own personal opinion.
> In general, by making RDFa less complex, it is likely to have more users.
> Right now, there is a multitude of ways to do a single thing, and this
> makes it hard for authors to remember which way is the right way, and also
> it makes it hard predicting which triples will be parsed. While the
> difficulty of the HTML5 parsing algorithm is to be expected due to
> deployment differences amongst massively deployed browsers, it seems when
> designing new technologies hoping for massive take-off simplicity should
> be a goal. And the current levels of use of RDFa are good and growing
> (hope we can get stats on that soon via Peter Mika), but it's still not a
> huge portion of the Web enough to justify unnecessary complexity due to
> backwards compatibility.  Machine-generation or authoring is not a
> solution, as RDFa will also have to be understood by the people writing
> the machine-generation scripts.
> Using people's cognitive constraints as 7 plus or minus 2, ideally a
> vocabulary should add 9 new things to a language. Right now RDFa adds 14,
> I suggest bringing it back down to 9. As backwards compatibilty with RDF 1
> is a goal, anything I am saying to removed can be kept in, but
> not-highlighted (i.e. not used in examples) and explicitly marked as kept
> in for backwards compability.
> Here's the comments:
> 1) Remove any reference to @href and @src to the XHTML and HTML5 documents
> about using RDFa. They do not really make sense in the core, as the are
> obviously specialized for use in making RDFa easier to use with a certain
> number of HTML elements, i.e. <a> and <img>. Having them in RDFa core
> needlessly complicates the document, and makes the parsing algorithm much
> more complicated. It's OK to keep them in XHTML or HTML5 profiles of RDFa
> for ease of hand-authoring I assume, although much of their work can just
> be done by use of <span> tags.
> 2) Please pick either @rel or @property for marking predicates, and do not
> encourage the use of both. This comment comes from Kavi Goel I imagine the
> use of both was caused by obscure features of HTML like the diff between
> <link>, <meta> and desire to stay XHTML compliant with <a>. These are no
> longer design goals, as now RDFa is just adding new attributes anyways.
> Based on feedback from Google RichSnippets, people get these two confused
> constantly. The supposed reason for keeping them apart is that @rel is
> supposed to point to URIs while @property points to literals. However, why
> not just use a simple EBNF for URI/IRIs to parse the object and *then* use
> that to determine if it's a URI or not? In the pathological edge-case
> where someone wants a URI to be parsed as a string rather than a resource,
> they can just add in the correct datatype using @datatype. In the even
> more pathological edge-case they rather have it parsed as a literal string
> rather than a xsd:string (and the fact that these are not the same in RDF
> is broken, obviously), one could add in "literal" as a datatype to handle
> that.
> Note that OGP already treats @property as something marking out URIs, not
> literals, i.e. from [1]:
> <meta property="og:url" content="" />
> <meta property="og:image"
> content="" />
> I'd ditch @rel, because as put by Kavi, it has two different possible uses
> -- it's either used on a link to another page, or to convey a relationship
> to another entity on the same page.
> 3) Similarly, pick either @resource or @content (or preferably, pick a
> better name like @object) and do not encourage the use of both for marking
> object. Again, the difference between @resource and @content is supposed
> to be to mark the difference between URIs and literals.
> 3) Please just pick one way to do vocabularies, and so eliminate the use
> of @vocab. Vocabularies should either reference an offline vocabulary
> profile for the namespace (@profile), or specify the namespace directly
> (@prefix). @profile serves a useful purpose of allowing prefixed CURIEs to
> be used. Of course, @prefix is needed for compatibility with HTML5. I do
> not really see any reason to add @vocab. Also, as a brief warning - was
> not @profile eliminated by HTML5, and used for a bunch of other things?
> Maybe just have @vocab be used for the current use of @profile if HTML5 is
> determined to keep @profile out.
> 4) Is there really a reason to have this inline use of @prefix="ex:
>"? I'd remove it. It makes misuse of URIs more
> likely, as Hixie is right on some things - people do not in general type
> URIs in correctly, usually things like a trailing # are forgotten.
> 5) Also, lots of people will forget to put the URI in the
> @prefix/profile/xmlns, but they tend to get things like "ogp:title" and
> "foaf:name" right in the content. Therefore, I suggest that the current
> rudimentary state of the XHTML profile be fixed, so that the top 10 or so
> vocabularies also have their namespaces stored there, so the common use of
> "foaf:name". Rather than hide that feature (I can barely find mention of
> the default XHTML profile [3] in the doc), it should be put in an example
> early on. Just using common namespaces with a centralized directory is a
> lot more sensible for end-users than putting expecting them to remember,
> or cut-and-paste, URIs correctly.
> 6) Lastly, as shown by OGP, there's two distinct use-cases for
> vocabularies, one where one is talking about the things a web-page is
> about, and the other a web-page. Right now RDFa is optimized to talk about
> the web-page. Is there a way we could add something to the vocabulary
> profile that says, "for this vocabulary, create a blanknode". Otherwise,
> say to use Facebook OGP correctly, one would have to a declare a blank
> node on top of the page, i.e. about="" or typeof="". I have to agree with
> David Recordon here, asking users to do something like that is a bit
> silly. It's better to have it in the vocabulary definition. You could
> easily add:
> <span property="rdfa:defaultresource">A blank node</span>
> Or if you want to give that a value (unlikely, but possible)
> <span property="rdfa:defaultresource"
> resource="">The default subject of this vocabulary
> is <a href=""></a>.</span>
> But you probably want to give it these blanknodes type:
> <span property="rdfa:defaultresource" typeof="abc:review">The default
> subject of this vocabulary is a blank node of type "review".</span>
> Speaking of that, we need a better description of the vocabulary profile
> parsing algorithm, it's kinda mentioned offhand the use of rdfa:uri and
> things like that, and it seems to be in this document [2]. Since it's
> important, why not just move that doc into core?
> 7) And since OGP has shown that many users find it easier to cut-and-paste
> <meta> and <link> into the head rather than annotate the body, why not
> show how that can be used as the first example *before* going into the
> body?
> 8) Also, I can't tell if this is allowed (again, thanks to Kavi for the
> example):
> Let's say I have a review about a restaurant. The markup to convey the
> relationship is:
> <span typeof="abc:Review">
>   <span rel="abc:itemReviewed">
>      <span typeof="abc:Restaurant">
> Microdata and microformats both remove one layer of nested html elements
> for this scenario. For example in microdata, it is:
> <span itemtype="">
>   <span itemprop="itemReviewed" itemscope itemtype="">
> And in microformats it would be shorter still:
> <span class="hreview">
>   <span class="item hrestaurant">
> Can we just have in RDFa?
> <span typeof="abc:Review">
>   <span rel="abc:itemReviewed" typeof="abc:Restaurant">
> I can't see why not, but not sure what the parsing algorithm does here.
>      cheers,
>            harry
> [1]
> [2]
> [3]
> [4]

Ivan Herman, W3C Semantic Web Activity Lead
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Received on Monday, 13 December 2010 09:58:41 UTC