W3C home > Mailing lists > Public > www-rdf-logic@w3.org > May 2001

Re: metadata vs. meta-(meta)-data

From: Sandro Hawke <sandro@w3.org>
Date: Mon, 21 May 2001 14:26:22 -0400
Message-Id: <200105211826.OAA14513@hawke.org>
To: "Larry Masinter" <LMM@acm.org>
cc: www-rdf-logic@w3.org
> I'm hoping that RDF can be modified in a way that
> distinguishes between the use of RDF to make assertions
> about actual web resources (data content) and its use
> to make assertions about things that are described or
> referenced by things on the net.
> 
> The use of "http" URIs as unique identifiers for things
> that are not resources backed by HTTP web servers is
> a serious confusion of levels.
> 
> The model for the sentence
> 
>  The students in course 6.001 are Amy, Tim, John, Mary, and Sue. 
>  is written in RDF/XML as
> 
> <rdf:RDF>
>   <rdf:Description about="http://mycollege.edu/courses/6.001">
>     <s:students>
>       <rdf:Bag>
> 	<rdf:li resource="http://mycollege.edu/students/Amy"/>
> 	<rdf:li resource="http://mycollege.edu/students/Tim"/>
> 	<rdf:li resource="http://mycollege.edu/students/John"/>
> 	<rdf:li resource="http://mycollege.edu/students/Mary"/>
> 	<rdf:li resource="http://mycollege.edu/students/Sue"/>
>       </rdf:Bag>
>     </s:students>
>   </rdf:Description>
> </rdf:RDF>
> 
> This example shows the confusion -- the description is not
> about the web page at http://mycollege.edu/courses/6.001, but
> it's about the course which is described by the web page at
> http://mycollege.edu/courses/6.001. However, we may also want
> to make assertions about the web page: when it was written,
> who wrote it, when it was last updated, where it is archived,
> etc.
> 
> The web page and the thing the web page is about are at
> different levels of quoting, but these levels are confounded
> in RDF today.
> 
> Adding a "#" at the end of the Description's about attribute's
> URI doesn't really help, since it resolves into the structural
> granuarity of the web page rather than into the next level of
> reference.

My understanding of RFC 2396 is that "#" only behaves that way
sometimes, eg for mime-type "text/html".  For another type, such as
"text/rdf" it might be defined differently.  In other words there
seems to be a technical loophole here; whether we want to use it is
another matter.

> I can think of several ways of fixing this, but they're all somewhat
> unpleasant:
> 
> - leave RDF as is, add another URI scheme that means
>   'the thing described by this URI'
>   <rdf:description about="ttdb:http://mycollege.edu/courses/6.001">
>   (ttdb - the thing described by )
> 
> - leave RDF as is, assume ttdb, and add a level of quoting if
>   you want to use RDF for metadata, e.g.,
>   <rdf:description about="data:text/uri,http://mycollege.edu/courses/6.001">
>
> - Define that each relationship should be specific about its level
>   of indirection, e.g., "dublin core RDF relations are about the
>   URI as a web resource, but other kinds of RDF assertions might
>   really about the thing described by the web resource rather than
>   the web resource itself".

Another alternative, of course, is to only use http: URIs when you're
talking about web pages, and use another scheme (eg my tag: scheme)
when you want to talk about something like a course or a student.   

    -- sandro
Received on Monday, 21 May 2001 14:26:28 UTC

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