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Re: [ALL] RDF/A Primer for review - Response to Gary Ng's Comments

From: Ben Adida <ben@mit.edu>
Date: Sun, 22 Jan 2006 19:36:47 -0500
Message-Id: <C02A21DB-1D98-4088-9DF4-66E39931212D@mit.edu>
Cc: SWBPD list <public-swbp-wg@w3.org>, public-rdf-in-xhtml task force <public-rdf-in-xhtml-tf@w3.org>
To: Guus Schreiber <schreiber@cs.vu.nl>


Guus,

Yes, we would like to ask the working group to approve moving the RDF/ 
A Primer to Working Draft status. We'd like to spend the 3-month  
extension to continue to get feedback from the WG and to add more  
examples.

If this vote can be squeezed into tomorrow's telecon agenda, that  
would be fantastic.

-Ben

On Jan 22, 2006, at 7:32 PM, Guus Schreiber wrote:

>
> Ben,
>
> Areyou in a position to propose the draft for WG publication?
>
> Best,
> Guus
>
>
> Ben Adida wrote:
>> Gary,
>> Thanks very much for your comments.
>> Please find the task force's responses below. Note that the  
>> responses  from Section 1 (Overall Organization) are from me  
>> alone, while the  responses to Section 2 (Design of RDF/A itself)  
>> are the result of  task force discussions from this week's  
>> telecon. We did not have time  to cover Section 1 in our telecon,  
>> so, as the primary author of the  Primer, I take it upon myself to  
>> answer those organizational  questions. The conceptual questions  
>> were discussed with everyone.
>>> It is a nice piece of work with clear intentions and examples. The
>>> principle of not duplicating content and embedding RDF content in  
>>> a  way
>>> browsers can extract is clearly articulated. The proposal with
>>> individual examples surrounding the photos and camera use case, plus
>>> showing their RDF equivalent is very informative.
>> Thanks!
>>> 1) Overall Organization
>>> =======================
>>>
>>> Would it be beneficial for the reader to have some brief   
>>> introduction on
>>> basic constructs, before diving into how they are used in the  
>>> use  case?
>>> I found it difficult to follow the examples without first have an
>>> overview understanding of (or knowing the boundary  
>>> surrounding...) the
>>> number of ways in which RDF can be specified, and using which
>>> constructs.
>>>
>>> For example, mid way through the doc, I found myself asking the
>>> question:
>>>
>>>     - "How about annotating tables, frames, forms and dynamic  
>>> content
>>> from scripts producing menus and flash?"
>>>
>>>     - "How do I create chains of triples?" For example, an  
>>> address  of a
>>> person (Mark in the example), represented by an annoymous node,   
>>> which in
>>> turn has statements specifying triples making up the address.
>>>
>>> These were answered after checking the RDF/A Syntax [1]. In fact,  
>>> the
>>> primer could effortlessly include these concepts only with a little
>>> introduction to the constructs.
>> We wrestled with this a bit, and we chose to keep the RDF/A  
>> Primer  short and example-focused, leaving the syntax description  
>> to the RDF/ A Syntax Document. The RDF/A Primer is definitely not  
>> meant to be  complete, but rather to give a taste of what RDF/A  
>> can do for you. If  the Primer raised questions that led you to  
>> the syntax document, then  that is a successful Primer, in my  
>> opinion.
>> Mark Birbeck is working on a set of even simpler examples to  
>> target  the blogging community. These would help introduce simple  
>> metadata  for HTML authors, before we even bring in RDF triples.  
>> I'll talk more  about this at Monday's telecon.
>>> 1.1) In the preliminaries, the following sentence may provide some
>>> initial context to the reader.
>>>
>>>      "An XHTML document marked up with RDF/A constructs is a  
>>> valid  XHTML
>>> Document. RDF/A is about using XHTML compatible constructs and
>>> extensions to specify RDF 'content'. It is not about embedding RDF
>>> syntax into XHTML documents."
>> Good suggestion.  We'll work this into the Primer.
>>> 1.2) With regards to the above questions I had while reading, I   
>>> suggest
>>> a small section right up front to introduce the basics, possible  
>>> with
>>> some simple examples from Section 3:
>>>
>>>      "id" and "about" - These are equivalent to rdf:id and  
>>> rdf:about.
>>> They can appear as xml attributes in any XHTML constructs,   
>>> including UL,
>>> LI, DIV, BLOCKQUOTES, P ... etc. They essentially declare a rdf   
>>> subject
>>> for constructing RDF/A statements, either locally within one  
>>> document,
>>> or made reference-able from other documents in the case of "id".
>>>
>>>      "link" and "meta" - These are the main constructs to create  
>>> rdf/a
>>> statements. Link is used to create a relationship to another URI
>>> resource, whereas meta is used to attach literal properties. These
>>> constructs can specify its own subject using "about", or they  
>>> take the
>>> immediate parent XHTML element's "about" as subject. In the case  
>>> where
>>> the immediate parent does not have qualifying URI, the subject is an
>>> anonymous rdf node. In the case where the immediate parent is a
>>> link/meta element without an "about" URI, this statement reifies the
>>> parent statement.
>>>
>>>      "anchor" and "span" - These are alternative constructs to  
>>> create
>>> rdf/a statements. While anchor can be used instead of link, span   
>>> can be
>>> used instead of meta. Their difference to link and meta is that  
>>> anchor
>>> and span applies to an 'inherited' rdf subject. The nesting   
>>> inheritance
>>> is identical to how xmlns attribute is inherited within an XML   
>>> document.
>>> If the nesting chain does not contain a qualified subject, the   
>>> document
>>> itself is the subject. These constructs allow the RDF content to
>>> somewhat follow the presentation of the content and thus avoid
>>> duplication.
>>>
>>>      Both meta and span each have two ways of specifying the   
>>> associating
>>> literal value. One is reusing what would also be displayed (the  
>>> CDData
>>> of the element):
>>>
>>>      <[span|meta] property="dc:date" type="xsd:date">2006-01-02</ 
>>> span>
>>>
>>>      The alternative is to use the 'content' attribute, where  
>>> the  value
>>> is not the the CDData and thus it is not displayed as well as being
>>> different to the CDData.
>>>
>>>      <[span|meta] property="dc:date" type="xsd:date"
>>> content="2006-01-02">XYZ</span>
>>>
>>>      In the latter case, if there is no CDData to display, this
>>> effectively attaches a piece of RDF that does not have any   
>>> presentation
>>> consequence. This symmetry is also observed with link and anchor.
>> This is very useful text, but it seems much more appropriate for  
>> the  RDF/A Syntax document. The Primer's role is really to  
>> introduce RDF/A  to an HTML audience that isn't expected to know  
>> much about RDF in the  first place. Jumping into a description of  
>> all the RDF concepts up  front seems a bit much for a Primer.
>> Again, I do think this is useful for the Syntax document, though.
>>> 1.3 Perhaps the primer should be arranged with a target reader  
>>> in  mind.
>>> For example, to arrange from the point of view of an HTML author   
>>> wanting
>>> to find out how to add annotations to his/her docs, in the  
>>> quickest  time
>>> possible.
>>>
>>> Primer How-to:
>>>
>>> A) say something about the Doc itself -
>>>
>>>   => essentially already in the examples within Section 3.
>>>   . examples on link and meta,
>>>   . examples on span and anchor,
>>>
>>> B) declaring individual elements contained in a doc, and say  
>>> something
>>> about them:
>>>
>>>   . Adding an id, currently embedded within section 4.3
>>>   . The use of about, currently embedded within section 4.2
>>>   . Then the usual way like above (A) to add metadata.
>>>   . Refering back to an id within the same doc.
>>>   . Refering an id in a different doc.
>>>
>>> C) say something about external content that the author has no  
>>> control
>>> over
>>>
>>>   => Currently 4.1
>>>   . Annotating href links,
>>>   . Annotating opague objects: images, scripts, objects
>>>
>>> D) Advanced Metadata
>>>
>>>   . using "link" and "meta" with unqualified XHTML elements,  
>>> creating
>>> chains of triples.
>> Yes, this is exactly what we're trying to do with the added  
>> examples  that Mark is developing. The only difference is that  
>> we're going to  stay away from talking too much about RDF graphs,  
>> and rather gently  guide the HTML author from adding simple  
>> properties to adding more  complex RDF statements.
>>> 1.4 Section 4.3 Qualifying chunks of document.
>>>
>>>      The title doesn't quite match the content here. The content is
>>> about how to declare elements and metadata (of individual  
>>> cameras  on one
>>> page) for other documents (photo album pages) to reference using   
>>> ids. It
>>> is still talking about annotating individual items (Cameras) in the
>>> document, and not chunks of document as a whole.
>> A good point. Again, I wonder how much HTML authors will really   
>> differentiate here, but the language should be clear  
>> nevertheless.  I'll work on this.
>>> 2) RDF/A itself.
>>> =============================
>>>
>>> I must say at first glance I found the approach extremely   
>>> confusing. RDF
>>> Mark up mixed with presentation markup such as <H1   
>>> property="dc:title">.
>>> But I appreciate that there aren't that many choices to avoid
>>> duplication of content, and to allow RDF markup within an orthogonal
>>> presentation structure.
>> Yes, there is bound to be some confusion at first. We're  
>> certainly  trying to minimize it - thus the limited scope of this  
>> primer.  Hopefully, by the time you finished reading the document,  
>> you were  less confused. But let us know if there are additional  
>> things we can  do (beyond your comments here) to reduce this  
>> confusion.
>>> 2.1) Synchronization issue between metadata on a doc, versus the
>>> metadata contained within that doc itself.
>>>
>>>     Images, files and other media will have their own metadata   
>>> embedded
>>> in the future. Certainly another html document will have its own
>>> metadata. If RDF/A allows metadata to be added locally about a  
>>> remote
>>> URL, potentially the local metadata could be out of sync, or worse
>>> contradict the metadata embedded within the resource itself?
>> This is indeed an issue of concern, though it appears to be one  
>> that  applies to all RDF serializations, including RDF/XML.  
>> Methods for  resolving such inconsistencies should be devised at a  
>> general RDF level.
>>> 2.2) Consistency
>>>
>>>      I suspect there may already be an answer to this: Why are we  
>>> not
>>> using rdf prefixed attributes for RDF/A elements/attributes? rdf:id?
>>> rdf:about? rdf:property, rdf:resource, rdf:description? This   
>>> relates to
>>> Pat's [2] comments about future migration from RDF to XHTML too.
>> The most important point here is that the task force tried hard  
>> to  use RDF/XML syntax for RDF/A, but this failed because of RDF/ 
>> XML's  striped syntax. Note also that reusing existing HTML  
>> attributes turns  out to make for a very good migration path for  
>> HTML authors (who  constitute the main target of this work.)
>> As per our response to Pat's comments, the right way to migrate  
>> large  chunks of RDF/XML into HTML is to use a <link rel="meta">  
>> element.  The hard part of the migration requires determining  
>> which rendered  data corresponds to which RDF property, and no  
>> amount of syntax can  help there: it's a semantic merging operation.
>>> 2.3)  How about inheriting metadata through nested elements?
>>>
>>> > In [2] Pat Hayes wrote:
>>> >
>>> > Also, giving an id to a whole RDF (sub)graph fits naturally
>>> > with the 'named graph' idea, unlike giving an id to every triple.
>>> >
>>>
>>> This is interesting and would qualify as "Qualifying chunks of
>>> document". For example, using some special non-presentational XHTML
>>> elements to "group" metadata together?
>> There may be a misunderstanding here. There *is* nesting in RDF/ 
>> A:  you can inherit the about attribute as far up/down the DOM  
>> hierarchy  as you'd like. Is that what you're after?
>>> 2.4) The <img> element not allowing child elements makes the  
>>> whole  RDF/A
>>> approach rather uneven. Is <img> the only XHTML element that does  
>>> not
>>> allow child element? could XHTML2 be changed to allow these meta   
>>> data to
>>> be the solely allowed child elements?
>>>
>>>     <li> <img src="/user/markb/photo/23456" />,
>>>       <span about="/user/markb/photo/23456" property="dc:title">
>>>         Sunset in Nice
>>>       </span>
>>>     </li>
>>>
>>>     Why don't we use the same approach instead of using <span>?
>>>
>>>     <img src="/user/markb/photo/23456" property="dc:title">
>>>       Sunset in Nice
>>>     </img>
>>>
>>>     of ocurse this now the subject is src="". But we can still  
>>> make  this
>>> work to say for img, the "about" is the "src" attribute. See 2.5   
>>> below.
>> This turns out to be one of our outstanding issues that we are  
>> still  finalizing. [1]
>> We are currently leaning towards the syntax you mention, where  
>> the  content of an image element could include metadata about that  
>> image  and the SRC attribute would be the subject. Steven is  
>> checking with  the XHTML working group to ensure that this does  
>> not cause any  unforeseen complications. However, what's important  
>> to note is that,  even if this syntax is adopted, the "Sunset in  
>> Nice" text in your  above example would only be rendered in a  
>> browser if there is a  failure to load the image.
>> This seems consistent with the fact that the image is really an   
>> external resource, and any internal HTML element value should  
>> really  be considered an ALT tag from the point of view of  
>> rendering. Note  that the same would apply to OBJECT elements.
>>> 2.5) Flexible subject/object referrals suggestion.
>>>
>>> Motivation 1:
>>>
>>>      One thing that RDF/A has not considered is the annotation of  
>>> HTML
>>> forms. Imagine sofware agents understanding the form semantically  
>>> and
>>> automagically carryout complex form filling (beyond username,   
>>> passwords
>>> and personal information) on behalf of the user. I believe forms'
>>> annotations will be extremely important for the semantic web.
>> Forms annotation is indeed important, and is already possible  
>> with  the current RDF/A. Remember that any XHTML element can be  
>> annotated.  What we should do is add an example in the primer to  
>> show how this  can be done, something along the lines of (this is  
>> XHTML1, just to  explain the principle):
>> ======
>> <form method="post" action="/foobar">
>>    <meta property="dc:description" content="Login Form" />
>>    <input type="text" name="username">
>>       <meta property="dc:title" content="username" />
>>    </input>
>> ...
>> </form>
>> =======
>> With proper annotations, browsers could become much smarter about   
>> what they do with these forms, as you mention.
>>> Motivation 2:
>>>
>>>      The use of content, href, about, id, are ways to specify the
>>> subject and the object/value of the rdf statements. I feel that   
>>> they are
>>> somewhat restrictive, especially when the author acknowledges  
>>> that  there
>>> are still some unavoidable duplication of content.
>>>
>>>      To further reduce duplication of URIs and literals, as well  
>>> as to
>>> cater for annotating HTML forms in the future, it would seem a more
>>> flexible approach may be possible.
>>>
>>>      Assuming the subject and object of the rdf statement can be  
>>> taken
>>> from existing XHTML (or XML) element attributes, one can completely
>>> avoid duplication by 'referring' to those attributes from  
>>> another, for
>>> example:
>>>
>>>      . <img src="http://....." attrAsStmtSubject="src">
>>>
>>>      . Normally the attrAsStmtSubject defaults to "about" and "id"
>>>
>>>      . <a href="http://....." attrAsStmtObject="href">
>>>
>>>      . Normally the attrAsStmtObject defaults to "href" and thus  
>>> could
>>> be unspecified.
>>>
>>>      . Similarly attrAsStmtValue="content",   
>>> attrAsStmtValue="CDData", or
>>> any other attributes/text element.
>>>
>>>       Although I have not worked out the details, but I believe  
>>> these
>>> three new attributes (attrAsStmtSubject and attrAsStmtValue/ 
>>> Object)  are
>>> compatible with RDF/A concepts, and I believe they will allow  
>>> forms to
>>> be annotated without much content duplication.
>> The task force feels that much of the motivations for these  
>> changes  could be accomplished without any additional complexity  
>> (see form  annotation above). Certainly, your suggestion would  
>> further reduce  data duplication, but only with significant added  
>> complexity in RDF/ A. Extracting triples would become far more  
>> complicated, as the  values of certain attributes would affect the  
>> actual parsing of the  rest of the document. Thus, at this point,  
>> we would not want to adopt  this recommendation.
>> Thanks for some very useful and insightful comments. Please let  
>> us  know if these answers give rise to new questions.
>> -Ben Adida
>> ben@mit.edu
>> [1] http://www.w3.org/2001/sw/BestPractices/HTML/2005-current- 
>> issues#src
>
> -- 
> Free University Amsterdam, Computer Science
> De Boelelaan 1081a, 1081 HV Amsterdam, The Netherlands
> Tel: +31 20 598 7739/7718; e-mail: schreiber@cs.vu.nl
> Home page: http://www.cs.vu.nl/~guus/
>
Received on Monday, 23 January 2006 00:37:03 UTC

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