W3C home > Mailing lists > Public > public-html-data-tf@w3.org > October 2011

Re: RDF 1.1 Lite Issue # 2: property vs rel

From: Stéphane Corlosquet <scorlosquet@gmail.com>
Date: Sun, 23 Oct 2011 00:42:57 -0700
Message-ID: <CAGR+nnGsM3P-93MwkXiOJRdd4kVfK=5UT1NpTCH+=odWSywUjQ@mail.gmail.com>
To: Ivan Herman <ivan@w3.org>
Cc: Gregg Kellogg <gregg@kellogg-assoc.com>, Ramanathan V Guha <guha@google.com>, Manu Sporny <msporny@digitalbazaar.com>, HTML Data Task Force WG <public-html-data-tf@w3.org>
(removing public-vocabs)

On Sun, Oct 23, 2011 at 12:34 AM, Ivan Herman <ivan@w3.org> wrote:

> Gregg,
>
>
> just for my understanding and concentrate on the most frequent @href/@src
> cases (the others are of a secondary importance compared to @href/@src). Can
> your rules be summarized as:
>
> - If, on an element, there is an @href/@src, there is a @property, but
> there is no @rel/@rev, then @property behaves like a @rel with @href in RDFa
> terms
> - In RDFa 1.1 Lite we advise users not to use @rel. Alternatively, @rel is
> not recognized in RDFa 1.1 Lite though still possible. (I would prefer the
> former, b.t.w.)
>
> I can see the value of this but, to be able to move ahead, we have to
> analyze the technical issues. Some that come to my mind immediately (I am at
> a conference now, unfortunately, so I have to divide my attention...):
>
> - If this is a general rule, I am not sure how we could use the textual
> content of a <a> element as a literal property. Well, it can be done by
> putting it in a separate <span> with all kind of other things.


I don't see this as a problem. Microdata has the same caveat, and <span> has
to be used inside <a> as well.

Steph.


> A possible, hack-style approach is to put a @rel="" on the element, which
> would push @property back on its traditional role.
>
> - I know I will sound as a broken record, but I am forced to beat this
> issue because it is still open. This works in microdata because the
> microdata spec introduced a special treatment for <link> (and <meta>)
> insofar as it allows <link> being part of the body if it uses microdata
> attributes. Until the same happens with RDFa attributes, the model above
> means that users can encode non-literal links (using RDF terms) only with
> clickable links (forget about the <head> now). Current HTML5 parser would
> move <link> to the head, unless I am mistaken (and I hope I am!), ie, it
> will not work.
>
> I am sure there are some others.
>
> B.t.w., admin issue: I wonder whether this discussion should continue on
> the vocabulary mailing list. It really becomes a syntax issue, ie, should
> move to the html task force (thanks for doing this) or the RDFa WG, or both.
> I would propose to remove the vocabulary task force cc in the future, unless
> others object...
>
> Thanks
>
> Ivan
>
>
>
>
>
> On Oct 23, 2011, at 02:28 , Gregg Kellogg wrote:
>
> > I'm CCing the HTML Data TF, as that's really the appropriate location for
> syntax discussions.
> >
> > I'm wondering if we could consider an HTML-specific approach to unifying
> @property and @rel in HTML+RDFa 1.1 Lite. Within that spec, we could define
> some additional processing rules for @property to create URIs, much
> (exactly) as MicroData does. This would not replace @rel, but the eventual
> RDFa 1.1 Lite specification/note would recommend that @rel NOT be used for
> markup for these use cases. Of course, if it were, the normal RDFa Core 1.1
> rules would apply.
> >
> > Microdata describes how to retrieve a property value [1]. The Microdata
> to RDF draft uses essentially the same, but with some additional detail for
> creating RDF [2]. Basically, elements that have an attribute with a URI
> content model use that value to create a URI Reference, and otherwise a
> literal is generated.
> >
> > * audio, embed, iframe, img, source, track, and video use the value of a
> @src attribute as a URI ref.
> > * a, area and link use the value of an @href attribute as a URI ref.
> > * object uses the value of a @data attribute as a URI ref.
> > * I also added rules for blockquote and q to use the value of a @cite
> attribute as a URI reference, but this is not in the HTML Microdata spec.
> > * Otherwise, @property acts as now defined in RDFa Core 1.1.
> >
> > Alternatively, we could say that @href, @src, @object and @cite take
> higher precedence and result in a URI ref from any element.
> >
> > Additionally, to allow for chaining, if @property were used in an element
> that also had either or both @about or @typeof, it would become a reference
> (URI or BNode) to a new object defined at that element scope, identically to
> @itemprop in the same element as @itemscope.
> >
> > HTML+RDFa 1.1 Lite could then adopt these same rules, so for example, a
> schema:Event might be marked up as follows:
> >
> > <div vocab="http://schema.org/" typeof="Event">
> >   <a property="url" href="nba-miami-philidelphia-game3.html">
> >   NBA Eastern Conference First Round Playoff Tickets:
> >   Miami Heat at Philadelphia 76ers - Game 3 (Home Game 1)
> >   </a>
> >
> >   <span property="startDate">2011-04-21T20:00</span>
> >
> >   <div property="Location" typeof="Place">
> >     <a property="url" href="wells-fargo-center.html">
> >     Wells Fargo Center
> >     </a>
> >     <div property="address" typeof="PostalAddress">
> >       <span property="addressLocality">Philadelphia</span>,
> >       <span property="addressRegion">PA</span>
> >     </div>
> >   </div>
> >
> >   <div property="offers" typeof="AggregateOffer">
> >     Priced from: <span property="lowPrice">$35</span>
> >     <span property="offerCount">1,938</span> tickets left
> >   </div>
> > </div>
> >
> > (Note, we miss some formatting with startDate, but if we were also to
> adopt @datetime processing rules, or whatever the HTML WG replaces it with,
> this could be handled better as well).
> >
> > There are probably some corner cases that would need to be worked out,
> but by limiting this to the HTML+RDFa definition, we avoid backwards
> compatibility issues with RDFa 1.0 and get that much closer
> >
> > Gregg
> >
> > [1] http://www.w3.org/TR/2011/WD-microdata-20110525/#values
> > [2]
> https://dvcs.w3.org/hg/htmldata/raw-file/24af1cde0da1/microdata-rdf/index.html#algorithm-terms
> >
> > On Oct 22, 2011, at 2:36 PM, Guha wrote:
> >
> >>
> >>
> >> On Sat, Oct 22, 2011 at 1:49 PM, Manu Sporny <msporny@digitalbazaar.com>
> wrote:
> >> On 10/22/2011 01:38 PM, Guha wrote:
> >> Google announced supported RDFa in 2009. One of the startling
> >> discoveries we made was that the error rate (i.e., webmasters marking
> >> up their pages to say X when the really meant to say Y) was about 3
> >> times as much as it was for other formats (which include
> >> microformats, sitemaps, Google shopping feeds, etc.). The error rate
> >>  is/was so bad that we had resort to highly non-scalable techniques
> >> like having humans look at the markup on each site to make sure it
> >> said what the page said. More than 40% of the errors had to do with
> >> the confusion between rel and property.
> >>
> >> That is startling. Could you please publish the data and analysis
> >> publicly so that those on this list may look at it and analyze it? We
> have a couple of approaches that we've discussed over the past 6+ years that
> could be applied if we knew exactly /how/ people were getting the markup
> wrong.
> >>
> >> We will look into sharing what we can. We have on a number of occasions
> shared aggregate data. It is not clear we are in a position to share
> detailed information about other people's websites. You are of course
> welcome to do the analysis yourself.
> >>
> >>
> >> I will also note that this particular data was never brought to the
> >> attention of the RDFa Working Group. When did you know about these
> >> errors? Why did you not share the data when you came across it? I ask
> >> because it would've impacted the design of RDFa 1.1 if you had shared
> >> this data with us at the time.
> >>
> >> Manu, I think you are missing something here. We have communicated this
> information, many times, in one-one meetings with Ben Adida and others as we
> were working on developing microdata. At the end of the day, it was
> negligence on the part of the folks designing RDFa 1.1 to not actively seek
> input from some biggest consumers of RDFa.
> >>
> >>
> >> It is important to note that this data is from a very large sample
> >> (10s of millions of pages) taken from Schema.org's target audience:
> >> webmasters of sites that are by and large not about technical stuff.
> >>
> >> A list of URLs would be great along with a technical analysis of all of
> >> those URLs. Specifically, the following data would be very helpful:
> >>
> >> Google DOES NOT provide lists of URLs to anyone. You are welcome to go
> crawl the web.
> >>
> >>
> >> * How frequent was the use of @rel vs. the use of @property?
> >>
> >> * When @rel was used, was it used in chaining or was it used to
> >>  simply refer to an external resource?
> >>
> >> We don't recommend chaining. Almost no one producing markup with rich
> snippets uses external resources.
> >>
> >> * In the Microformats and Creative Commons cases
> >>  (rel="license", rel="tag", etc.) did people get @rel wrong?
> >>
> >> You should ask them.
> >>
> >> * How frequently does @rel and @property exist on the same element?
> >>
> >> In the vocabulary we specified, never.
> >>
> >> * How frequently is @property used when @rel should have been used
> >>  instead?
> >>
> >> Don't have the numbers, but it was pretty random. You have to understand
> that at anything more than a few percent error rate, the data becomes
> largely unusable in scale.
> >>
> >> * How frequently is @rel used when @property should have been used
> >>  instead?
> >>
> >> I will look into doing this analysis, but am not sure when we will be
> able to get around to this.
> >>
> >>
> >> Answering these questions will help us understand how the spec should
> change.
> >>
> >>
> >> We really don't want to get into whether there is a distinction
> >> between rel and property at a theoretical level.
> >>
> >> Who is "we" in this case? The RDFa WG does not want to get into a
> theoretical debate either. We care about authors easily generating good,
> valid data.
> >>
> >> We = Google, Schema.org.
> >>
> >>
> >> But the bottom line remains that as long as
> >> the error rate in RDFa usage does not go down dramatically, it is not
> >> a viable option for us.
> >>
> >> Who is "us" in this case?
> >>
> >> Us = Google, Schema.org
> >>
> >>
> >> The current proposal takes a step in the
> >> right direction, but several big issues, like the removal of the
> >> distinction between rel and property still need to be addressed.
> >>
> >> Could you please detail every one of those "big issues"?
> >>
> >> We are doing it. Jason brought up the other issue.
> >>
> >> -- manu
> >>
> >> --
> >> Manu Sporny (skype: msporny, twitter: manusporny)
> >> Founder/CEO - Digital Bazaar, Inc.
> >> blog: Standardizing Payment Links - Why Online Tipping has Failed
> >> http://manu.sporny.org/2011/payment-links/
> >>
> >>
> >
>
>
> ----
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> PGP Key: http://www.ivan-herman.net/pgpkey.html
> FOAF: http://www.ivan-herman.net/foaf.rdf
>
>
>
>
>
>
Received on Sunday, 23 October 2011 07:43:26 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Sunday, 23 October 2011 07:43:27 GMT