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

RE: rdfms-resource-semantics

From: Lee Jonas <lee.jonas@cakehouse.co.uk>
Date: Wed, 6 Jun 2001 12:18:35 +0100
Message-ID: <51ED29F31E20D411AAFD00105A4CD7A77132@ZINGIBER>
To: "'Brian McBride'" <bwm@hplb.hpl.hp.com>
Cc: "'www-rdf-interest@w3.org'" <www-rdf-interest@w3.org>
Brian McBride [mailto:bwm@hplb.hpl.hp.com] wrote:
>
>Hi Lee,
>
>I'm sorry for the tardy response.  Email overload again.  Here are some
>preliminary thoughts..
>
>Lee Jonas wrote:
>> 
>> Are there no thoughts at all on this [1] from the RDF Core WG?
>
>> 
>> [1]
>> http://lists.w3.org/Archives/Public/www-rdf-comments/2001AprJun/0105.htm
>> l
>> 
>> regards
>> Lee
>
>[...]
>
>>Why bother defining a special RDF notion of 'resource'?  After all, it
>>conflicts with the definition in RFC2396 causing much confusion and a
>>special RDF definition of 'resource' is probably unnecessary anyway.
>
>Quite so.  I don't want to have a special RDF notion of resource either.
>But I would like there to be a well defined and well understood one
>for the entire web.  
>
>
>And I think there is some confusion about what
>exactly a resource is which goes well beyond RDF.
>

Although I sympathise with this desire on a personal level, it could be
considered beyond the RDF Core WG's charter.  I am proposing a way to
unencumber RDF (esp. the RDF M&S specification) from "philosophical" debates
about what resources (and fragments) actually are, consigning them to
discussions of RFC2396.

This one *alignment* change may simplify or even cut out many issues that
are rooted in the interpretation of RDF resources, fragments, mime-types,
etc.

>If we are to be clear about RDF means, and RDF is about describing
>resources, then its important to be clear about what a resource is.
>

I agree. However, I argue that the definition of resource is already given
in RFC2396.  It may sound like a cop-out, but for all their problems,
URI-references are a cornerstone that is fundamental to the Internet, which
RDF could consider atomic.  End of story.  As argued, this kind of 'reuse'
of RFC2396 acutally goes a major step towards conformity with other Internet
and XML standards, and cuts out any confusion over whether you are talking
about a 'Resource' in the RFC2396 sense or the RDF sense, which is a major
bugbear that will only hamper RDF adoption.

>>Rather than shoehorn the notion of 'resource' into what the RDF M&S spec
>>requires as a primary building block, you could turn the problem around
and
>>define RDF M&S in the existing terms of RFC2396.  Within RDF M&S:
>>
>>1) Describe RFC2396 as 'normative'.
>>2) substitute all occurrences of the word 'resource' for the word
>>'reference' (or something similiar).
>>3) define 'references' as the union of URI references and anonymous
>>constructs.
>>4) refer readers to RFC2396 for the URI reference definition.
>
>That may be a useful approach.  Does RFC 2396 tell me whether the
>two different URI's can name the same resource?  Does it define a 
>notion of equivalence?
>

There are aspects of URIs that would not factor into any equivalence test,
e.g. port number.  Conversely there may be other factors
that should be incorporated, such as multitypes for a given resource (e.g.
is 'doc.html.en' equivalent to 'doc.html.fr'?).

However, for the most part, equivalence is scheme specific.  From RFC2396:

[[
6. URI Normalization and Equivalence

   In many cases, different URI strings may actually identify the
   identical resource. For example, the host names used in URL are
   actually case insensitive, and the URL <http://www.XEROX.com> is
   equivalent to <http://www.xerox.com>. In general, the rules for
   equivalence and definition of a normal form, if any, are scheme
   dependent. When a scheme uses elements of the common syntax, it will
   also use the common syntax equivalence rules, namely that the scheme
   and hostname are case insensitive and a URL with an explicit ":port",
   where the port is the default for the scheme, is equivalent to one
   where the port is elided.
]]

So the answers to your questions are 'yes' and 'yes'.  IMHO, any further
specification of URI-equivalence would benefit the community more if it were
in a separate RFC or W3C Note (i.e. not specific to RDF).

>>That way, RDF's 4 sets become 'Statements', 'Literals', 'References' and
>>'Properties'.
>>
>>This has the following plus points:
>>1) it avoids the name collision with RFC2396 resources altogether (rather
>>than having to explain a special interpretation of 'resource').
>
>I don't think we are looking to have a special interpretation of resource.
>We just want to be clear what it means.
>

The RDF M&S spec defines its own notion of 'Resource' that conflicts with
RFC2396.  I could be wrong, but the discussions I have seen on w3c-rdf-core
indicate that you are considering changing the spec to define RDF
'resources' in terms of RFC2396.  But I am suggesting you go a step further
and eliminate the special RDF notion of 'resources' altogether - It is
unnecessary when RDF can talk about describing URI references instead.

>>2) it integrates RDF better with existing web technologies, adopting
>>standard semantics for URIs and network entities.
>
>Absolutely.
>
>>3) it shifts the emphasis of RDF to the description of resource views /
>>parts of resources (i.e. fragments).  (But, who cares whether metadata
>>assertions are about RDF resources or RFC2396 resource views technically -
>>in practise they still have the same effect).
>>4) RDF can still be considered 'Resource Description' - only now it is
>>description of resources and their views/parts in the RFC2396 sense.
>>5) It won't break existing applications - the RDF syntax won't change as
>>'Resource' is not part of the language.  It could even be considered just
an
>>editorial fix to the spec.
>
>What you suggest is a change to the RDF formal model.  I don't think it
>can be considered just an editorial fix.
>

I have to admit I was a bit dubious about making this point - nothing is
ever that straightforward ;-)

However, at its simplest, I am proposing s/Resource/Reference in the RDF M&S
spec.  It is a change in terminology - the model and syntax remain
unchanged.

[snip]

regards

Lee

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end
Received on Wednesday, 6 June 2001 07:18:02 GMT

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