- From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
- Date: Thu, 31 Jan 2013 15:21:03 +0100
- To: public-rdfa-wg@w3.org
Ivan Herman: > Olaf, > > To be honest, I am not sure how to solve these issues, and I would welcome > your suggestions. Well, at least the XHTML+RDFa variant of 'HTML5' should have the version attribute, I think, 'HTML5' is anyway only for tag soup processing, therefore not useful for documents intended to survive a long time. The version attribute is in the XHTML namespace anyway, just because it is not mentioned in the current HTML5 draft does not mean, that it vanishes from the XHTML namespace. An improvement for the syntax of the value could be to allow an URI to something, that defines exactly, what this version means and how to interprete the document. Another not very practical option could be, that authors use RDFa attributes, that reference the definition of the element in the related (X)HTML specification whatever version this is - this could implicate that all children follow this specification, if not redefined with another RDFa attribute value. One can do this for all elements deviating from the defined meaning of the parent element. One can construct of course more advanced meta information using RDFa on a meta element, in doubt referencing an external specification, what a version of a format means. If required, maybe I can write an external specification of a format version indication - this can be referenced with RDFa to define the meaning of an RDFa attribute referencing a specification as a resource or something like this ;o) Obviously current viewers will fail to interprete this correctly, but this is our experience with (X)HTML viewers anyway for all versions of (X)HTML, that they do not get it completely right - therefore no surprise for advanced authors and readers ;o) However, in doubt everyone can analyse the source code manually to find out the intended meaning of the document, that is independent from the interpretation of viewers. And the method is risky - if I or someone else decides to switch off the server with the specification of the format version indication, things get undefined again - therefore better to have a more stable internal definition. The logical problem of this approach is of course, that one has to interprete first the related RDFa attribute to be able to follow the reference to the definition of the meaning of such an attribute ;o) Typically such formal things are not a big problem for human interpreters of such documents, therefore this is still usable as a makeshift/stopgap, if the HTML5 working group does not manage to solve the version indications problem (what is quite probable, because they did not solve it in the past years, therefore effectively still one cannot write HTML5-documents at all ;o) A simpler approach without direct logical problems is to use as suggested an DCMI term within a meta element referencing applicable specifications. But this is a solution relying on a specification out of the domain of W3C - therefore another makeshift/stopgap for an internally unsolved problem. Interestingly the profile attribute seems to be removed as well in the HTML5 draft, that is or was required to define the meaning of meta information with DCMI - looks like another indication, that HTML5 is not intended for documents with relevant content, only for tag soup ;o) But of course, the HTML+RDFa draft adds anyway the RDFa attributes to the HTML5 draft, why not a version attribute as well? If it is ok to add attributes like property, content, about etc, what is the problem with version, if it turns out, that this is essential to get defined semantics? Yet another option could be a generic XML mechanism (another than DTDs) to reference the specification applicable for the current document. Obviously it turns out, that it is not sufficient only to indicate the namespace, one has to add a version information as well, if there is more than one version and different features within the namespace have slightly different meanings in different versions (if this appears as for (X)HTML, this may indicate anyway, that the specificators already failed, but because nobody is perfect, it is reasonable to care about such problems in practice). The mechanism could be similar to the XML (stylesheet) processing instruction. This does not solve the problem for HTML5 itself, but authors wanting to publish relevant content could simply only use the XML-variant. > We face two problems here. > > In (X)HTML5 the @version attribute does not exist any more. In previous > versions of RDFa we made use of that attribute and, actually, RDFa 1.1 Core > still refers to this attribute for, eg., XHTML1.0. Processors hitting the > @version value referring to RDFa 1.0, for example, are supposed to process > accordingly. But, as I said, this option is not available any more in > (X)HTML5... > > Of course, we could define a separate attribute, much like we do have a > number of RDFa 1.1 attributes. But there comes the next issue: many > authors, or indeed 'webmaster advices' issued by companies like Facebook, > ignore that attribute anyway. The practice is that authors do not use it. > Ie, we did not want to rely on the presence of such attribute to control an > RDFa processor. Meaning that we have to define a behaviour in the absence > of any additional hints. > One cannot define the meaning of any arbitrary tag soup as HTML5 tries to do, there will always be some nonsense remaining. And because there is currently no version indication method in HTML5, every author, that follows such a draft only creates tag soup documents without a defined meaning ;o) I do not worry about such nonsense documents, that often disappear within a few months or years. If the document has no indication, there is no urgent need for an RDFa processor to get a detailed and correct interpretation of the content ;o) Obviously one can say, that the tag soup is always interpreted with the newest RDFa variant, implicating, that such documents have no time independent meaning at all ;o) I think, it is more important to allow authors to write documents with a defined meaning at all, if they want. And this implicates, that such authors need to indicate the version of the document format they use, else they are not able to write something better than meaningless tag soup. And the probabilty, that one has an author wanting to publish documents with a defined meaning increases, if such an author uses RDFa attributes, indicating already some care about semantics and meaning of the content. > So... > > On Jan 31, 2013, at 11:54 , "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de> wrote: > > Hello, > > > > the working draft > > http://www.w3.org/TR/2012/WD-rdfa-in-html-20121213/ > > as well as this variant from today > > http://www.w3.org/2010/02/rdfa/sources/rdfa-in-html/ > > contain in section 3.1 the sentence: > > "Documents served as application/xhtml+xml, that don't contain a DTD, and > > don't specify a @version attribute must be interpreted as XHTML5+RDFa 1.1 > > documents." > > > > Does this mean, that if for example in 20 years I write an XHTML6+RDFa > > 2.0 document, there will be a DTD or version indication again to ensure, > > that the document will be interpreted as XHTML6+RDFa 2.0 and not as > > XHTML5+RDFa 1.1? > > Hopefully RDFa 2.0 would be backward compatible with RDFa 1.1, ie, it would > not matter (although I know this is not 100% sure with RDFa 1.0/1.1 :-(. Who knows, what the future will bring, may more or less wisdom ;o) Already the minor differences here show, there is a need for authors so be able to specify the version they use. > And if this is not the case, then indeed some new attributes may have to be > used. Actually, this issue will come up regardless of RDFa: What will > happen with XHTML5 vs. XHTML6? Maybe some mechanism will be introduced by > the HTML WG of the time to ensure that.... If every version has a new mechanism to indicate, to which version a document belongs to and (X)HTML5 has none, this causes logical problems as well. Obviously one has always to know the complete history of (X)HTML to find out, what the document could mean - and documents without version indication will remain without defined meaning, because those existed already before the first draft for HTML5 was written, therefore one cannot rely on the claim, that no indications means HTML5 - it can be any tag soup. The indication with a DTD or an URI allows at least to discover the intentions again, if one knows, what specification documents were available with these identifiers. Such a mechanism is required, therefore the method with version="XHTML+RDFa 1.1" was already suboptimal, should have been version="http://www.w3.org/TR/2012/REC-xhtml-rdfa-20120607/" or something related. > > > How to indicate precisely, that a document is of version XHTML5+RDFa 1.1, > > because section 2.1 only notes: > > "XML mode XHTML5+RDFa 1.1 documents should be labeled with the Internet > > Media Type application/xhtml+xml as defined in section 12.3 of the HTML5 > > specification [HTML5], must not use a DOCTYPE declaration for XHTML+RDFa > > 1.0 or XHTML+RDFa 1.1, and should not use the @version attribute." > > > > This does not implicate, how to indicate an XHTML5+RDFa 1.1 at all. > > Doesn't this finally mean, that one effectively cannot write an > > XHTML5+RDFa 1.1 document at all, because one cannot indicate, that > > the document follows this version? > > I am not sure I follow your argument. XHTML5+RDFa 1.1 is the 'default' for > application/xhtml+xml, unless a DTD says otherwise (ie, points at XHTML1 > and/or RDFa 1.0). Of course, if it uses a DTD, it is not XHTML5 any more, > but it can still be XHTML1.1. Well, XHTML+RDFa currently does not require a DTD, and if XHTML documents had no DTD in the past, but the namespace was indicated correctly, it was still application/xhtml+xml without any relation to HTML5, because HTML5 did not exist in the past. Therefore a future specification of HTML5 cannot change the meaning of documents publish before, this would result in nonsense. HTML5 can only suggest an interpretation for documents without a relation to a specific version, but this does not implicate, that HTML5 can define the meaning of such documents. The content type only is not sufficient to provide information about the version of the format, because there is only one content type, but many versions of XHTML. This is similar to interpretations of a poem - there can be many interpretations, but only if the author points to a document with the intended interpretation, we can learn something about the intended meaning. Arbitrary interpretations contain always a mixture of the intentions of the interpreter and the work itself, what can be interesting as well, but not necessarily to get the intentions of the authors. The same applies, if arbitrary documents are interpreted with the HTML5 draft - can be interesting, but not necessarily what was intended ;o) > > Again, this is primarily an (X)HTML issue, ie, an issue of XHTML5 vs. > XHTML1.1. RDFa just follows the XHTML5 rules here... If we assume, that HTML5 is intended for tag soup only and XHTML+RDFa for semantically relevant content, this creates a big difference. We do not have to worry about authors only wanting to create HTML5 tag soup. But for XHTML+RDFa authors there is an important need to indicate clearly, what they use, because at least some of them care about semantics and defined meanings. Therefore a version indication might be neglectable for HTML5, but not for XHTML+RDFa. And presumably if HTML5 ever will become a recommendation, there will be authors wanting to switch from XHTML+RDFa 1.0/1.1 to a newer version, but without version indication in the new variant they cannot, they stuck in a trap and have maybe to consider to switch to a complete different format again, because up-to-date (X)HTML versions become unavailable for top quality content. > > Ivan > > > Or should one indicate the relation for example with a DCMI Term > > (http://dublincore.org/documents/2012/06/14/dcmi-terms/) > > like conformsTo or format with the URI of the specification as value? > > Is this the currently preferred approach for all types of > > (X)HTML5-documents, because they currently have no version indication > > itself? > > Or is there a simpler method without the need of other formats to > > indicate, that one has an (X)HTML5 document and not something else? > > > > > > Olaf > > ---- > Ivan Herman, W3C Semantic Web Activity Lead > Home: http://www.w3.org/People/Ivan/ > mobile: +31-641044153 > FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Thursday, 31 January 2013 14:27:24 UTC