- From: Guus Schreiber <schreiber@cs.vu.nl>
- Date: Mon, 23 Jan 2006 02:19:20 +0100
- To: Ben Adida <ben@mit.edu>
- CC: SWBPD list <public-swbp-wg@w3.org>, public-rdf-in-xhtml task force <public-rdf-in-xhtml-tf@w3.org>
Ben, Yes, I will. Can you send mail to the list about the status/location of the version we should decide about? Thanks, Guus Ben Adida wrote: > > 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/ >> > -- 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 01:19:35 UTC