- From: Danny Ayers <danny@panlanka.net>
- Date: Wed, 18 Apr 2001 12:51:01 +0600
- To: "Murray Altheim" <altheim@eng.sun.com>, "Seth Russell" <seth@robustai.net>
- Cc: "Dan Brickley" <danbri@w3.org>, "Joshua Allen" <joshuaa@microsoft.com>, "Sean B. Palmer" <sean@mysterylights.com>, "RDF Interest" <www-rdf-interest@w3.org>
Just a thought - what we are more or less saying by embedding RDF in a doc is that 'here is some metadata, process it if you can', so might not a PI play a role here? (presumably in combination with NOTATIONs) --- Danny Ayers http://www.isacat.net <- -----Original Message----- <- From: altheim@mehitabel.eng.sun.com <- [mailto:altheim@mehitabel.eng.sun.com]On Behalf Of Murray Altheim <- Sent: 18 April 2001 06:18 <- To: Seth Russell <- Cc: Dan Brickley; Joshua Allen; Sean B. Palmer; Danny Ayers; RDF <- Interest <- Subject: Re: RDF in XHTML <- <- <- Seth Russell wrote: <- > <- > From: "Murray Altheim" <altheim@eng.sun.com> <- > <- > > I've never offered to solve world hunger, even for RDF <- flesh. I don't know <- > > how to solve that one. The *only* way I can imagine (that <- wouldn't involve <- > > an act of Congress) would be to have CDATA section nodes <- containing RDF be <- > > notation-marked as RDF, such that they get passed off to an <- RDF schema <- > > processor for *appropriate* processing. This isn't <- technically all that <- > > difficult, but it's religiously and politically unlikely. IMO. <- > <- > Actually this solution is rather attractive to me ... it has <- the smell of <- > the right way to do it. But I'm a babe in the woods where it comes to <- > swimming in these waters. Could you (or somebody) sketch the <- theological <- > implications for us? <- <- Theologically, it seems to me that few people in the W3C like the SGML <- approach to dealing with non-XML content, which would be to use <- notations. <- Their way would be using XML namespaces, which unfortunately <- don't provide <- the features that XML notations do. You'd use XML Schema datatypes, which <- is a might bit more complex. <- <- The XML Schema approach is also markedly different, which is to <- *validate* <- the content. Notation-based approaches simply indicate what previously- <- declared notation a specific entity is considered to be, "entity" in our <- case being a CDATA-wrapped DOM node. <- <- XML 1.0 got halfway there in supporting SGML notations, in that one can <- indicate the notation of element content, but one cannot do this for <- attribute content. Given that most theologians believe that element and <- attribute content are both "document content" this was an unfortunate <- oversight that would have allowed DTDs to compete with XML Schemas on a <- more level playing field. I'd like to see any update of XML include <- notations on attributes, but I'm a bit cynical given the W3C's dislike <- of DTDs. <- <- But for our purposes here, what we have will do just fine. Check out the <- following if you want to follow along in the XML spec as to I'm talking <- about: <- <- http://www.xml.com/axml/target.html#Notations <- <- Basically, we can't simply put any markup that contains angle brackets <- into any XML document without breaking validity. XHTML is not special <- in this regard. But we can wrap such markup (such as RDF) in a CDATA <- section. This means that it doesn't get well-formedness checking, which <- would have to occur in the processor that receives the CDATA section <- DOM node. But if this was an understood part of the process, we could <- proceed. <- <- In the DTD we'd have something akin to: <- <- <!NOTATION dc PUBLIC <- "-//DCMI//NOTATION Dublin Core Metadata Element Set V1.0//EN"" <- "http://dublincore.org/"> <- <!NOTATION rdf SYSTEM "http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <- <!NOTATION blat PUBLIC "-//doctypes.org//NOTATION Blat 1.0//EN" <- "http://www.doctypes.org/blat/1.0/"> <- ... <- <!ELEMENT metadata ( #PCDATA ) > <!-- really, a CDATA section --> <- <!ATTLIST metadata <- type NOTATION (dc|rdf|blat) <- > <- ]><!-- end of DTD --> <- ... <- <head> <- <metadata type="rdf"> <- <![CDATA[ <- {rdf content} <- ]]></metadata> <- <- The "(dc|rdf|blat)" list can't unfortunately be an open-ended list. <- Each of the tokens in the list must be a declared NOTATION in the DTD, <- otherwise you'll get an error. But given the purpose of DTDs is to create <- constraints, this isn't too bad; this is essentially a contract to <- everyone on what we'd all accept in terms of available public notations. <- We could add a empty parameter entity to allow it to be extended in a <- document's internal subset for custom or development use, such as: <- <- <!ENTITY % Metadata.ext ""> <- <!ATTLIST metadata <- type NOTATION (dc|rdf|blat %Metadata.ext;) <- > <- <- Then, as I mentioned above, the CDATA section DOM node (ie., the content <- of the metadata element) would be passed off to processor which would <- strip off the CDATA section wrapper and pass it to another XML parser <- process, which would first well-formedness check it before sending it <- off to the RDF processor. If the RDF was of a particular known <- application, <- it would then process the content appropriately. Any decent <- engineer could <- whip this up in fairly short order from commonly available tools. [Okay, <- so I've outlined the process...] <- <- > > Why do you need to have the RDF be *in* the XHTML file? <- Honestly, without <- > > trying to sell you an XTM solution, this is precisely what <- XTM is good <- > > for: mapping resources within XML files. [..good stuff snipped...] <- > <- > Well for the general solution to describing resources with RDF <- we need to be <- > able to read and write it ... were working on the writing ... <- the reading <- > (first level) will need to be just as simple. Ideally a <- browser plug-in or <- > the browser itself can pop up a surfable user friendly window of the <- > metadata. Knowing the XTM tags and retrieving other resources <- is going to <- > complicate that application an order of magnitude. Imho, it's a deal <- > breaker. <- <- I wasn't trying to make it a bar to entry, only pointing out a possible <- solution. RDF could be used for this too, but one would need a specific <- application of RDF to standardize the semantics of the mapping, and you'd <- have something *like* XTM then. And I'm not particularly interested in <- creating a custom RDF language to use for mapping web documents. I'll <- bet somebody else is, and I'm not one to rein on anyone's parade here. <- <- > > As has been mentioned in other threads and by other people, creating <- > > external documents means more document management, less document <- > portability, <- > > the likelihood of metadata-document mismatch, etc. People <- already spend <- > too <- > > much time managing (or not managing) their document sets. <- I'd hate to add <- > > to their burden. <- > <- > I agree. I seem to smell a consensus that the embedded way is <- the best ... <- > it's just that there is this theological problem with it, and it's <- > currently politically incorrect. Well shucks .. we stopped <- the war, didn't <- > we, so this should be an easy piece. <- <- Embedding DC won't be too bad. Embedding RDF will require also a software <- solution that's a tad bit custom currently in the XML world: actually <- paying attention to notation declarations and passing content off to <- notation processors. Oh, and in having an RDF notation process know to <- cast off the CDATA wrapper prior to beginning processing. There's no <- spec that spells out this process; perhaps there should be. But I do <- maintain that the solution I've described above is likely unpalatable <- to the W3C. I'd be happy to be shown wrong, though. <- <- Murray <- <- PS. I'm cc'ing myself as I just did a substantial amount of the <- DTD work. :-) <- BTW, isn't everyone on the cc list also on RDF Interest? Why not <- kill the cc <- and rely on the listserver? I'm getting an awful lot of duplicates. <- ................................................................. <- .......... <- Murray Altheim, SGML/XML Grease Monkey <mailto:altheim@eng.sun.com> XML Technology Center Sun Microsystems, 1601 Willow Rd., MS UMPK17-102, Menlo Park, CA 94025 the wood louse sits on a splinter and sings to the rising sap ain't it awful how winter lingers in springtimes lap -- archy
Received on Wednesday, 18 April 2001 02:55:17 UTC