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Re: how do I copy some properties that are part of a bigger pattern

From: Jarno van Driel <jarnovandriel@gmail.com>
Date: Tue, 11 Mar 2014 15:41:09 +0100
Message-ID: <CADK2AU3gwBUhQPMzjUDjoj7OzRy581jNAqQdwo3n0yXv5v6WUw@mail.gmail.com>
To: Gregg Kellogg <gregg@greggkellogg.net>
Cc: Niklas Lindström <lindstream@gmail.com>, public-rdfa <public-rdfa@w3.org>
Thanks for the sources Gregg. Some of 'm I know but with the new insights I
have now I bet some of 'm will make much more sense to me now. I'll make
sure to read it before asking more questions.


2014-03-11 2:01 GMT+01:00 Gregg Kellogg <gregg@greggkellogg.net>:

> On Mar 10, 2014, at 5:07 AM, Jarno van Driel <jarnovandriel@gmail.com>
> wrote:
>
> "...There is no difference here between links and "nested" items..." +
> "...Try the example..."
> Thanks, you just made my brain explode.   =)
>
> It's been a couple of years since my first attempts at understanding RDFa
> - which failed miserably - since I have difficulty translating the W3
> specifications in, for me, understandable rules on how it's supposed to be
> used and what it can do. Your comments together with the RDFa Play outcome
> succeeded where countless hours of reading specifications and experimenting
> with markup have failed me. Seriously Niklas, thanks!
>
> Now as for the IRC meet, let that slide for now. A tsunami of
> possibilities just flushed over me and I have to give it some time to let
> it sink in. The first thought I had after reading your comments and seeing
> the RDFa Play outcome was that writing an article about the use of @itemref
> isn't that difficult but comparing that to rdfa:pattern just became a whole
> lot more complicated. It now has become clear to me there is no 1:1
> relation between the two - where I thought there was - and that RDFa offers
> different solutions for many of the situations where one only can use
> @itemref in Microdata. Which IS marvelous but which leaves me confused in
> how to clarify that in an article without writing a series that's as thick
> as the bible.
>
>
> There are some great discussion threads on public-rdfa-wg in around
> December 2012, starting with a proposal from Ivan. Check out the
> "Reproducing Gregg/Niklas' thoughts ..." thread in
> http://lists.w3.org/Archives/Public/public-rdfa-wg/2012Dec/thread.html.
>
> As Niklas points out, the original concept was that a semantic approach to
> property-copying, where we identified a resource and used it as the source
> for copying properties, and remove the original "template" resource.
> Basically, it could mostly be done using SPARQL with INSERT DATA/DELETE
> DATA. It's worth looking at the thread to see some of the thought processes
> that were going on at the time.
>
> I do know however that I want to limit myself to RDFa Lite since it's the
> RDFa community's answer to Microdata. Or at least that's way I understand
> it. So let me therefore ask, what are the differences between RDFa and RDFa
> Lite? Is there any clear documentation about the difference between the two
> I can read?
>
>
> The RDFa Lite 1.1 recommendation <http://www.w3.org/TR/rdfa-lite/> pretty
> much calls this out. Also, the RDFa 1.1 Primer <
> http://www.w3.org/TR/xhtml-rdfa-primer/>. The key observation to the LIte
> recommendation is that RDFa gets complicated when there are too many
> attributes on an element, and the distinction between @about and @resource
> can be subtle. Even now, I see people having a problem with Microdata, when
> they use @itemprop on an anchor, and seem to expect the content of the
> element, rather than the value of @href to be used as the property's value.
> RDFa suffers from the same issue, but things get simpler when you restrict
> yourself to using fewer attributes and avoid combining them together.
>
> That said, there is quite a bit of power in full RDFa 1.1, particularly in
> the use of lists and chaining <http://www.w3.org/TR/rdfa-core/#s_chaining>.
> Chaining is really useful when you have a number of resource values from
> the same property, for example the author list of a document. This avoids
> repeating markup, but it is a sophisticated feature. IMO, you really can't
> write RDFa (full or lite) or Microdata without running it through a
> distiller to verify that it says what you mean.
>
> Let me widen the question: Are there any sources you guys can recommend me
> to read about RDFa (Lite)?
> Like I said earlier, it's been a couple of years for me, so I hope new
> documentation exists by now, besides the W3 specifications.
>
>
> Manu wrote a great post on the differences between RDFa Lite and
> Microdata: <http://manu.sporny.org/2012/mythical-differences/>.
>
> Gregg
>
> 2014-03-09 18:10 GMT+01:00 Niklas Lindström <lindstream@gmail.com>:
>
>> Hi Jarno,
>>
>> On Sun, Mar 9, 2014 at 5:08 PM, Jarno van Driel <jarnovandriel@gmail.com>wrote:
>>
>>> "...outputs two different nodes for what seemingly is the same
>>> corporation..."
>>> You're right in stating that this results in two instances of the same
>>> Corporation. Which is the only way in Microdata to have an Item
>>> (Corporation) be linked to other Items by means of different properties
>>> (copyrightHolder & publisher). The following markup simply wouldn't work in
>>> Microdata:
>>> <div itemprop="manufacturer" itemref="corporation-data">
>>>
>>
>> Yes, microdata (presumably) being a tree model prevents it from
>> connecting items together naturally. It's a big flaw. It only deals with
>> surface data, and says nothing about what it means. Perhaps @itemid makes
>> it into some kind of graph at times though, it's hard to tell when there
>> are no semantics explaining what that entails.
>>
>>
>> In Microdata itemref can only get additional info about a Type. You can't
>>> use it on a property and then use itemref to get the @itemtype elsewhere.
>>> That's why in Microdata I have to declare the Corporation twice, to be able
>>> to link it to different entities (ItemPage & Article) by means of different
>>> properties (copyrightHolder & publisher). Which brings me to the question:
>>> Can this be accomplished RDFa Lite where it can't in Microdata? - keeping
>>> in mind that in this specific example according to schema.org rules the
>>> publisher and copyrightHolder are both expected to 'have' a type and are
>>> not supposed to 'link' to a type.
>>>
>>
>> Yes, it can. RDFa uses the RDF data model, which is a graph [1]. There is
>> no difference here between links and "nested" items. You type and (when
>> needed) identify things, link them together and describe their details with
>> literals (texts) - all using properties. That is what I did in the example
>> given.
>>
>>
>> "...<p resource="#page">
>>> <span property="copyrightHolder" typeof="Corporation"
>>> resource="#corp">..."
>>> The downside to this method is that the copyrighHolder-Corporation now
>>> gets linked falsely. I quickly checked the output in Google's SDTT, which
>>> showed the Corporation being a child of the WPFooter as opposed to being
>>> the copyrightHolder of the ItemPage. The use of rdfa:pattern prevents this
>>> happening as does a itemscope without an itemtype in Microdata e.g. <div
>>> itemscope>.
>>>
>>
>> The Google SDTT is wrong. It should recognize that <p resource="#page">
>> sets the subject for nested statements (here ensuring that the <#page> has
>> the <#corp> as :copyrightHolder). It seems that adding a @typeof:
>>
>>     <p resource="#page" typeof="ItemPage">
>>
>> makes it behave somewhat more as expected. But note that that isn't
>> necessary in RDFa, it's just a workaround for a bug in the SDTT. (Try the
>> example out in e.g. <http://rdfa.info/play/> to see it more clearly.)
>>
>>
>>
>>> "Also, the resulting data here doesn't contain two distinct nodes for
>>> what is apparently meant to be the same corporation."
>>> True, but the two distinct nodes also have type-specific relations to
>>> the two distinct items this example has, namely ItemPage and Article. Maybe
>>> that info got a bit lost because I stripped out so much of the original
>>> HTML. The source I took this from has an ItemPage with a gazillion other
>>> types attached to it while the Article is just that, an Article, with it's
>>> own set of properties, mostly separated from the rest of the content on the
>>> ItemPage, only sharing data from the Corporation.
>>>
>>
>> I think I see how you mean. But if you think of this in terms of the RDF
>> data model, the items simply are resources linked together (and assigned
>> some types, and described with textual properties), rather than blocks of
>> data tied to the page structure (or the microdata tree structure, which
>> hardly helps). In this model, the corporation is surely one thing,
>> connected to from the ItemPage using copyrightHolder, and from the Article
>> using publisher (both of which are fine since the thing linked to is of the
>> expected type).
>>
>>
>>
>>> "I'd be happy to take a look at such examples as well."
>>> Maybe we should meet in an IRC session, like Gregg suggested, because
>>> I'm convinced we can keep this argument-counterargument up for quite some
>>> time. Not that I mind, since this mailing has already given me a ton to
>>> think about, but simply to be more time-efficient. Just let me know what
>>> you guys prefer, either way is fine with me.
>>>
>>
>> I'm fine either way too. :) I tend to have intermittent bouts of time, so
>> mailing is usually better for examples. But I could go for a chat over
>> specifics if needed.
>>
>> Cheers,
>> Niklas
>>
>> [1]: http://www.w3.org/TR/rdf11-primer/
>>
>>
>>
>>>
>>>
>>> 2014-03-09 14:19 GMT+01:00 Niklas Lindström <lindstream@gmail.com>:
>>>
>>> Hi Jarno and Gregg!
>>>>
>>>> It seems to me that this is a good example of where @itemref-like
>>>> functionality is quite unnecessary in RDFa. The #copyright-holder simply
>>>> contains a link from the page to the corporation, and the #publisher-url
>>>> and #publisher-description contain properties of that corporation. The
>>>> resulting microdata, however, outputs two different nodes for what
>>>> seemingly is the same corporation, so perhaps the example has been
>>>> simplified too much, thus obscuring what is actually needed?
>>>>
>>>> Still, In RDFa, instead of adding different @id:s to disparate parts of
>>>> the page which are about the same resource (and then listing them in
>>>> @itemref), you simply use @resource to capture the fact that a given block
>>>> is about it.
>>>>
>>>> Your example can thus be written like this in RDFa Lite:
>>>>
>>>> - - - 8< - - -
>>>>
>>>> <body vocab="http://schema.org/" typeof="ItemPage" resource="#page">
>>>>   <article property="text">
>>>>     <div typeof="Article">
>>>>       <link property="publisher" resource="#corp">
>>>>
>>>>       <h1 property="name">How to copy properties in RDFa Lite &
>>>> Microdata</h1>
>>>>     </div>
>>>>   </article>
>>>>
>>>>   <footer property="mentions" typeof="WPFooter">
>>>>     <div property="text">
>>>>       <p resource="#page">
>>>>         <span property="copyrightHolder" typeof="Corporation"
>>>> resource="#corp">
>>>>           <a property="url" href="http://www.example.org">
>>>>              <span property="name">Corporation name</span>
>>>>           </a>
>>>>
>>>>           <span property="description">Corporation description</span>
>>>>          </span>
>>>>       </p>
>>>>     </div>
>>>>   </footer>
>>>> </body>
>>>>
>>>> - - - >8 - - -
>>>>
>>>> In my opinion, this is a more convenient way of handling data smeared
>>>> out in a messy tag soup (with the results being shorter and more
>>>> legible). Of course, you need to name these resources, unless they already
>>>> have formal URIs, but that's easily done with a fragment identifier or a
>>>> bnode id. (And note that in microdata, you instead need to ensure that a
>>>> layout designer doesn't meddle with the @id values used by @itemref, for
>>>> quite different reasons (their use in CSS and JS).)
>>>>
>>>> Also, the resulting data here doesn't contain two distinct nodes for
>>>> what is apparently meant to be the same corporation.
>>>>
>>>> Remember, it is only when you need to duplicate a set of properties for
>>>> different resources that rdfa:copy is necessary. And even in those
>>>> circumstances, you might be able to leverage the way @resource can group
>>>> descriptions together, to build up one pattern from disparate parts of the
>>>> page.
>>>>
>>>> I'd be happy to take a look at such examples as well.
>>>>
>>>> Cheers,
>>>> Niklas
>>>>
>>>>
>>>>
>>>> On Sun, Mar 9, 2014 at 11:51 AM, Jarno van Driel <
>>>> jarnovandriel@gmail.com> wrote:
>>>>
>>>>> I think your and my latest example just passed each other Gregg. I
>>>>> guess I posted mine when you were writing yours because when I compare the
>>>>> two I see we implemented the same workaround by means of additional
>>>>> @resource.
>>>>>
>>>>> "I wouldn't recommend the use of included patterns in RDFa, but it
>>>>> can be made to work."
>>>>> I wouldn't recommend it either but unfortunately the everyday website
>>>>> out there consists out of a HTML-soup which doesn't allow for Semantic
>>>>> markup to be added in a nice and clean way. Now I mainly work on already
>>>>> existing websites, where I have to make do with HTML that's already in
>>>>> place. Therefore itemref or rdfa:pattern are indispensable when
>>>>> organizing/linking data that's smeared out over many different HTML
>>>>> elements on a page. I am very aware this results in markup that isn't
>>>>> 'nice' but it helps create meaning even if the HTML is a mess.
>>>>>
>>>>> "P.S., I think it's great that you're trying to describe this for a
>>>>> wider audience!"
>>>>> Well, I'm not doing it alone. Aaron Bradley is acting as the devil's
>>>>> advocate by asking me questions which mess up the solutions I provide.
>>>>> Which in return forces me to come up with different solutions and ask a lot
>>>>> of questions at the public-vocabs (and now here as well).   :)
>>>>>
>>>>> So trying to do something for a bigger audience will most definitely
>>>>> end up in something that has been contributed by many people. As always
>>>>> this kind of stuff ends up being a multi-community/person effort since it
>>>>> brings together so many different specializations and specifications.
>>>>>
>>>>> --
>>>>>
>>>>> Andy and Gregg,
>>>>> Thanks for sharing your knowledge, I'll make sure re-share it and am
>>>>> hopeful it will result in an article (or series of) which will try to serve
>>>>> anybody who is (or should be) interested in this type of info.
>>>>>
>>>>>
>>>>> 2014-03-09 6:46 GMT+01:00 Gregg Kellogg <gregg@greggkellogg.net>:
>>>>>
>>>>> On Mar 8, 2014, at 5:50 PM, Jarno van Driel <jarnovandriel@gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>> "..the @resource attributes get in the way.."
>>>>>> Could you explain this to me a bit more please Gregg? Because if I
>>>>>> parse my last markup through the Structured data linter and RDFa Play I get
>>>>>> 100% the same outcome as with your markup. Yandex and Google see the same
>>>>>> data as well (in a ever so slightly different manner).
>>>>>>
>>>>>> When I look at the output these parsers have no trouble extracting
>>>>>> the @resources as different rdfanodes. Unless I'm completely overlooking
>>>>>> something, or am breaking some cardinal rules, which both are feasible
>>>>>> since I just got around to looking more deeply into RDFa Lite.
>>>>>>
>>>>>>
>>>>>> In order to be able to reference the publisher-uri and
>>>>>> publisher-description information as patterns, they need to have an
>>>>>> identifier, which I supplied by adding @resource (and
>>>>>> @typeof="rdfa:Pattern) to each. However, this changes the scope of their
>>>>>> properties relative to the copyright-holder.
>>>>>>
>>>>>> In you're RDFa version you weren't able to access the publisher-uri
>>>>>> or publisher-description, as you do from Microdata. The RDFa property
>>>>>> copying uses a resource of type rdfa:Pattern, which must be identified as a
>>>>>> resource. For this reason, I added the @resource and @typeof for both the
>>>>>> publisher-description and publisher-url. However, doing that, changes the
>>>>>> current subject for each of these, so the "url" and "description"
>>>>>> properties are allocated to different resources. To get around this, I
>>>>>> added the rdfa:copy properties both the the publisher reference, and to the
>>>>>> copyright-holder, so that the properties appear in each of them. I wouldn't
>>>>>> recommend the use of included patterns in RDFa, but it can be made to work.
>>>>>>
>>>>>> I'd recommend both for Microdata and RDFa to keep references simple,
>>>>>> and using included references, while possible, can make things more
>>>>>> confusing. This is certainly not a pattern we were concerned about when
>>>>>> crafting the property copying mechanism in HTML+RDFa. They two really work
>>>>>> quite differently: Microdata requires full access to the DOM so that
>>>>>> referenced elements can be copied, which requires random access to the DOM.
>>>>>> The RDFa mechanism operates at a semantic level, by creating triples as
>>>>>> normal. RDFa is intended to work with streaming processors, where there is
>>>>>> no random-access to the DOM. The spec provides details of the rules which
>>>>>> are applied to achieve the effect of property copying [1], but it's not
>>>>>> really magic to RDFa, and could just as easily be done for triples
>>>>>> extracted from Turtle, or even Microdata, if the appropriate copying rules
>>>>>> were applied.
>>>>>>
>>>>>> I understood that you didn't know how to deal with a pattern embedded
>>>>>> in another pattern, which I attempted to address for you. I think that the
>>>>>> RDFa I provided does essentially what your Microdata does. If you want to
>>>>>> discuss more, we should probably meet on IRC.
>>>>>>
>>>>>> Gregg
>>>>>>
>>>>>> P.S., I think it's great that you're trying to describe this for a
>>>>>> wider audience!
>>>>>>
>>>>>> [1] http://www.w3.org/TR/rdfa-in-html/#implementing-property-copying
>>>>>>
>>>>>>
>>>>>> 2014-03-09 1:33 GMT+01:00 Gregg Kellogg <gregg@greggkellogg.net>:
>>>>>>
>>>>>>> Hi Jarno, I don't think you can do precicely what you want, since if
>>>>>>> a pattern is included in another pattern, the @resource attributes get in
>>>>>>> the way. You can do it by adding some more rdfa:copy properties. This is
>>>>>>> what I came up with:
>>>>>>>
>>>>>>> <body vocab="http://schema.org/" resource="#item-page"
>>>>>>> typeof="ItemPage">
>>>>>>>   <link property="rdfa:copy" href="#copyright-holder">
>>>>>>>
>>>>>>>   <article property="text">
>>>>>>>     <div resource="#article" typeof="Article">
>>>>>>>       <div property="publisher" typeof="Corporation">
>>>>>>>         <link property="rdfa:copy" href="#publisher-url"/>
>>>>>>>         <link property="rdfa:copy" href="#publisher-description"/>
>>>>>>>       </div>
>>>>>>>
>>>>>>>
>>>>>>>       <h1 property="Name">How to copy properties in RDFa Lite &amp;
>>>>>>> Microdata</h1>
>>>>>>>     </div>
>>>>>>>   </article>
>>>>>>>
>>>>>>>   <footer property="mentions" typeof="WPFooter">
>>>>>>>     <div property="text">
>>>>>>>       <p resource="#copyright-holder" typeof="rdfa:Pattern">
>>>>>>>         <span property="copyrightHolder" typeof="Corporation">
>>>>>>>           <link property="rdfa:copy" href="#publisher-url"/>
>>>>>>>           <link property="rdfa:copy" href="#publisher-description"/>
>>>>>>>           <span resource="#publisher-url" typeof="rdfa:Pattern">
>>>>>>>             <a id="publisher-url" property="url" href="
>>>>>>> http://www.example.org" title>
>>>>>>>               <span property="name">Corporation name</span>
>>>>>>>             </a>
>>>>>>>           </span>
>>>>>>>
>>>>>>>           <span resource="#publisher-description"
>>>>>>> typeof="rdfa:Pattern">
>>>>>>>             <span id="publisher-description"
>>>>>>> property="description">Corporation description</span>
>>>>>>>           </span>
>>>>>>>         </span>
>>>>>>>       </p>
>>>>>>>     </div>
>>>>>>>   </footer>
>>>>>>> </body>
>>>>>>>
>>>>>>>  Gregg Kellogg
>>>>>>> gregg@greggkellogg.net
>>>>>>>
>>>>>>> On Mar 8, 2014, at 2:37 PM, Jarno van Driel <jarnovandriel@gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>> <body vocab="http://schema.org/" resource="#item-page"
>>>>>>> typeof="ItemPage">
>>>>>>> <link property="rdfa:copy" href="#copyright-holder">
>>>>>>>
>>>>>>> <article property="text">
>>>>>>> <div resource="#article" typeof="Article">
>>>>>>>   <link property="publisher" typeof="Corporation" href=?????>
>>>>>>>
>>>>>>>  <h1 property="Name">How to copy properties in RDFa Lite &
>>>>>>> Microdata</h1>
>>>>>>> </div>
>>>>>>>  </article>
>>>>>>>
>>>>>>> <footer property="mentions" typeof="WPFooter">
>>>>>>>  <div property="text">
>>>>>>>  <p resource="#copyright-holder" typeof="rdfa:Pattern">
>>>>>>>  <span property="copyrightHolder" typeof="Corporation">
>>>>>>>   <a id="publisher-url" property="url" href="http://www.example.org"
>>>>>>> title>
>>>>>>>   <span property="name">Corporation name</span>
>>>>>>>  </a>
>>>>>>>
>>>>>>> <span id="publisher-description" property="description">Corporation
>>>>>>> description</span>
>>>>>>>  </span>
>>>>>>>  </p>
>>>>>>>  </div>
>>>>>>> </footer>
>>>>>>> </body>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
>
Received on Tuesday, 11 March 2014 14:41:42 UTC

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