W3C home > Mailing lists > Public > www-rdf-interest@w3.org > April 2001

Re: Common Metadata (was:RE: RDF in XHTML)

From: Gustaf Neumann <neumann@wu-wien.ac.at>
Date: Fri, 20 Apr 2001 23:00:29 +0200
To: "Danny Ayers" <danny@panlanka.net>, "Brian McBride" <bwm@hplb.hpl.hp.com>
Cc: "RDFInterest" <www-rdf-interest@w3.org>
Message-Id: <0104202300292F.08446@mohegan.wu-wien.ac.at>
On Friday 20 April 2001 18:47, Danny Ayers wrote:
> Thanks for your reply, but I can't say that I'm particularly reassured. You
> mention ways of possibly bending aboutEachPrefix and seeAlso into use. You
> also give reasons why these aren't exactly ideal. You refer to a syntactic
> include mechanism - have you got an existing one in mind, or woud this
> need, erm... including?
>
> Let me suggest another scenario - I have 10000 documents on cheesemaking,
> 5000 of these are by the same author, 5000 by another, half of the
> documents are from one publisher half from another (not along author lines
> or anything). You will surely agree that this metadata doesn't represent
> much information. Ok, perhaps I could dynamically generate metadata,
> perhaps I could hack XSLT to do what I wanted. Or of course I could repeat
> the same information 10000 times inline with all the documents.
>
> The model for what's ideally needed is multiple inheritance, or at least
> something approaching this. 

 i believe that ***sharing*** of the information is the way to go.
 you will have a registry for a cheesmaker factory that produces
 something like
  
  <Cheesmaker rdf:ID="cm999">
     <name>....</name>
     ...
  </Cheesmaker>

 and you refer from the cheesmaker to the appropriate cheesmaker ID.
 this is similar to good old normalization and might require 
 something like a JINI like service.

 best regards
-gustaf

> From what your saying there is no 'natural' way
> of doing this with RDF as it stands. If there might a relatively
> straightforward way using what's already available, all well and good,
> otherwise there's going to be some hassle not far down the line. Is this
> deserving of a 'see also' at the bottom of the rdfms-abouteachprefix issue?
> Maybe not. But I'm going to be looking at topic maps a bit more closely
> from now on...
>
> Cheers,
> Danny.
>
>
> ---
> Danny Ayers
> http://www.isacat.net
>
> <- -----Original Message-----
> <- From: Brian McBride [mailto:bwm@hplb.hpl.hp.com]
> <- Sent: 20 April 2001 21:45
> <- To: Danny Ayers
> <- Cc: Lee Jonas; Murray Altheim; RDFInterest
> <- Subject: Re: Common Metadata (was:RE: RDF in XHTML)
> <-
> <-
> <- Hi Danny,
> <-
> <- So the problem is, "How is common metadata to be represented in RDF
> <- XML?" and you give a good example.
> <-
> <- Two ideas have been suggested: using aboutEachPrefix and using seeAlso.
> <-
> <- There is an issue listed regarding aboutEachPrefix:
> <-
> <-   http://www.w3.org/2000/03/rdf-tracking/#rdfms-abouteachprefix
> <-
> <- One of the problems is that aboutEachPrefix is described in the syntax
> <- but is not described in the model.  This is pretty dodgy ground at the
> <- moment because a lot of systems don't implement it.
> <-
> <- Even if one were to use aboutEachPrefix, where would the XML for those
> <- statements be?  In a separate document?  How would a system find that
> <- document, given one of your 1000 pages?
> <-
> <- Regarding seeAlso, the definition of seeAlso states:
> <-
> <-   The property rdfs:seeAlso specifies a resource that might provide
> <-   additional information about the subject resource.
> <-
> <- So an RDF processor is not required to follow the link, but could do so.
> <- However, what do you put in the see also document?
> <-
> <-   <rdf:RDF>
> <-     <rdf:Description about="WHAT">
> <-       <dc:creator>foo bar</dc:creator>
> <-     </rdf:Description>
> <-   </rdf:RDF>
> <-
> <- The problem is that the value of the about attribute is absolute, it
> <- does not change its meaning depending on what link you followed to get
> <- it.  So
> <- that doesn't seem to do what you need.
> <-
> <- A combination of seeAlso and aboutEachPrefix might do it.  Put the
> <- seeAlso in each document and use aboutEachPrefix in the 'see also'
> <- document.  But as I said, aboutEachPrefix is not widely implemented.
> <-
> <- A syntactic include mechanism might do what you are looking for.  It
> <- might then include say:
> <-
> <-   <rdf:RDF>
> <-     <rdf:Description rdf:about="">
> <-       <dc:creator>foo bar</dc:creator>
> <-     </rdf:Description>
> <-   </rdf:RDF>
> <-
> <- Note the rdf:about.  There are problems here.  First, a robot finding
> <- the file to be included would see that it was created by foo bar, which
> <- might well not be true.  Secondly, XML isn't too good at being nested in
> <- other XML at the syntactic level because of issues with things like
> <- uniqueness of ID's and namespace prefix usage.
> <-
> <- However, for the range of things under your control, you could arrange
> <- to
> <- do this with say, an XSLT transform, to insert the meta data
> <- automatically.  This is not really an RDF solution.  If I had an
> <- immediate problem, I think this is the way I'd go.
> <-
> <- In terms of the issue list, I suggest you have highlighted an aspect
> <- of the rdfms-abouteachprefix issue, and I'd propose to add a reference
> <- to this thread under a 'see also' link under that issue.
> <-
> <- Brian
> <-
> <-
> <-
> <- Danny Ayers wrote:
> <- >
> <- > I can't see how RDF could be practical without some mechanism for
> <- > inherited/shared metadata (you've got a 1000 documents with the same
> <- > author - do you need to specify this a 1000 times), but I'm
> <- thinking that
> <- > because this is so significant it must have been dealt with already -
> <- > seeAlso doesn't really seem adequate, I'm not sure of the history of
> <- > aboutEachPrefix, but surely there is already some mechanism in
> <- place? Lee's
> <- > xsl:include/import suggestion sounds possible. If this angle is well
> <- > covered, an idiot's guide is needed (for this idiot at least),
> <- otherwise I
> <- > think it could well be an issue.
> <- >
> <- > ---
> <- > Danny Ayers
> <- > http://www.isacat.net
> <- >
> <- > <- -----Original Message-----
> <- > <- From: www-rdf-interest-request@w3.org
> <- > <- [mailto:www-rdf-interest-request@w3.org]On Behalf Of Lee Jonas
> <- > <- Sent: 20 April 2001 19:47
> <- > <- To: 'Danny Ayers'; Murray Altheim
> <- > <- Cc: RDFInterest
> <- > <- Subject: RE: RDF in XHTML
> <- > <-
> <- > <-
> <- > <-
> <- > <-
> <- > <- Danny Ayers [mailto:danny@panlanka.net] wrote:
> <- > <-
> <- > <- ><- The RDF Schema spec hints at 'rdfs:seeAlso' for
> <- cascading purposes,
> <- > <- e.g.:
> <- > <- ><-
> <- > <- ><- <rdf:RDF ...(namespaces)...>
> <- > <- ><-  <rdf:Description rdf:about="" rdfs:seeAlso="furtherinfo.rdf"/>
> <- > <- ><- </rdf:RDF>
> <- > <- >
> <- > <- >Looks viable - I wonder if there's anything more than hints
> <- > <- >this is rather important, probably well known (but I can't
> <- > <- think of it) -
> <- > <- >what is the best way to use inheritance of metadata
> <- between documents?
> <- > <- >How do I avoid adding the same author information to every
> <- one of the
> <- > <- >million pages I've written (with the aid of some monkeys)?
> <- > <- >
> <- > <-
> <- > <- Well, this is an entirely different prospect, and one I
> <- think that the
> <- > <- 'rdf:aboutEachPrefix' predicate was intended to address.
> <- > <- However, AFAIK it
> <- > <- has a lot of opposition due to the fact that it is difficult to
> <- > <- implement in
> <- > <- practise, e.g.:
> <- > <-
> <- > <- 1) Consider starting with a resource and trying to determine who
> <- > <- the author
> <- > <- was.  If this info is in a 'rdf:aboutEachPrefix' statement in
> <- > <- some other rdf
> <- > <- doc, not even referenced from the resource you are currently
> <- > <- processing, it
> <- > <- is nigh on impossible to determine.
> <- > <-
> <- > <- 2) It relies upon the hierarchical location of resource
> <- representations -
> <- > <- the granularity of what these kinds of statements apply to is
> <- > <- too course -
> <- > <- i.e. all resources whose URIs 'startWith' a common substring. It
> <- > <- might have
> <- > <- been better to do something akin to what XPointer does for XML.
> <- > <-
> <- > <- Suggestion:
> <- > <- IMHO rdf:seeAlso is equivalent to xsl:include semantics.  What
> <- > <- is lacking is
> <- > <- xsl:import semantics.  The latter might allow you to define a set
> of <- > <- statements that apply to their current doc, then 'importing' <-
> > <- that doc from
> <- > <- another would make those same statements apply to the doc doing the
> <- > <- importing.  Hence, importing a handful of rdf docs containing
> common <- > <- statements (e.g. author) from a million XHTML web pages
> would <- > <- save a lot of
> <- > <- typing!
> <- > <-
> <- > <- This would solve both 1) and 2) above to some degree of
> <- > <- satisfaction - the
> <- > <- degree of satisfaction of 2) depends on how you structure
> <- your imported
> <- > <- docs.  Is this worthy of the issues list?
> <- > <-
> <- > <- >
> <- > <- >
> <- > <- ><- >On another line, forget XHTML for a moment, how do we embed
> <- > <- metadata in
> <- > <- ><- >other XML markups?
> <- > <- ><-
> <- > <- ><- I thought this is what XML Namespaces are for!  Just embed your
> <- > <- elements,
> <- > <- ><- any processor that doesn't recognise the namespace (within its
> <- > <- ><- context) can
> <- > <- ><- ignore it.  Note that to validate such documents
> <- properly (and allow
> <- > <- such
> <- > <- ><- open mixing-and-matching of different 'XML mini-languages')
> will <- > <- ><- require XML
> <- > <- ><- Schema.
> <- > <- >
> <- > <- >Quite. (to avoid this going in circles, please ignore) so why
> <- > <- should XHTML
> <- > <- >be treated any different?
> <- > <-
> <- > <- One reason is that it is currently validated using a DTD.
> <- Whether XML
> <- > <- Schema would fare better, I don't altogether know for sure.
> <- > <-
> <- > <- (Note that my current understanding of XML Schema is not
> <- perfect, I am
> <- > <- hoping that XML Schema allows you to freely mix-and-match
> <- elements in
> <- > <- different XML namespaces.)
> <- > <-
> <- > <- regards
> <- > <-
> <- > <- Lee
> <- > <-
> <-
Received on Friday, 20 April 2001 17:01:21 GMT

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