W3C home > Mailing lists > Public > www-rdf-interest@w3.org > April 2003

Re: URI for language identifiers

From: Jan Algermissen <algermissen@acm.org>
Date: Tue, 01 Apr 2003 12:43:57 +0200
Message-ID: <3E896D6D.B54DD93D@acm.org>
To: Patrick.Stickler@nokia.com
Cc: www-rdf-interest@w3.org

Patrick.Stickler@nokia.com wrote:

> > Example: If the predicate is from Dublin Core, the subject is allways
> > the webpage, never an abstract concept.
> Well, actually, DC doesn't say that, neither explicitly by any domain
> assertion nor in any of the prose descriptions/comments of the subject
> property. So I don't see where you're getting that. 

Well, I take it as implicit in the semantics of Dublin Core. In other words:
If I want to make sense of an RDF statement that has a DC predicate I need to
know those semantics.

But for the sake
> of argument, let's just presume that there is something akin to
>    dc:subject rdfs:domain ex:WebPage .
> > I know, that is not RDF-ish thinking ;-)
> Well, actually, it is.
> If a predicate has a domain defined for it, then it is quite OK to
> infer a type characteristic of any subject used with that predicate.
> I.e., the use of the subject with that predicate is an implicit
> assertion that the subject is of the particular type per the specified
> domain.

So, it would make sense for the DC folks to make these things explicit,
to publish them as an RDF document?

> *HOWEVER*, even if one may infer that implicit assertion based on
> the domain of the predicate, that doesn't necessarily mean it is correct.
> The authority/owner of the subject may in fact not agree with such
> an assertion and  there may very well be authoritative
> information about the subject which conflicts with the assertions
> inferred from its use with a given predicate.
> No *use* of the subject with a given predicate counts as any authoritative
> assertion about the nature of that subject.
> If http://www.w3.org/Consortium in fact denotes a web page, no amount
> of usage with the property http://foo/directory is going to change that
> and make it denote an organization -- insofar as the authoritative
> definition of the resource is concerned.

Now, this seems complicated to me... oh well ;-)

> > Huh...does that mean that 'proper' use or RDF does not allow me to use
> > addresses of existing web pages to refer to abstract
> > concepts?
> If those URIs denote web pages, then no, you certainly should not
> use those URIs to denote any other resource, abstract or otherwise.
> > That seems
> > like a severe limitation to me? Of what use is an identifier
> > if I cannot
> > use for example HTTP GET to 'see/read' what it means?
> If a URI denotes an abstract concept, you may be able to GET a
> representation of that resource. Why not.

This is a thing I just don't get about RDF. I find it VERY strange that
a document can be a representation of a dog. But I guess that is just
something to accept as part of the (re-)definition of resource if I
want to use RDF.

Furthermore as it prohibits an author to use "http://www.w3.org/Consortium/"
as an identifier for the W3C (since it is a Web page).

> > No, in TM land, a URI allways is the address of 'the web page', a URI
> > *never* addresses an abstract concept.
> Well, that wasn't my understanding. But if that's true, then TMs and
> RDF are even farther apart than I thought.

> > Then in TMs URIs can be used as subject indicators, refering to
> > arbitrary subjects.
> And how do you then make statements about the 'web page' versus
> the subject? If you are using the same URI?
> > A key concept is that when the URI of a
> > subject indicator
> > is dereferenced and the retrieved information resource is
> > rendered for human
> > perception it should be clear what subject the URI indicates.
> But how do you differentiate between dereferencing the URI as
> a subject indicator versus dereferencing the URI as a web page,
> and is there any logical relationship between the web page
> denoted by the URI versus the subject indicator denoted by the
> same URI?

> Having this ambiguity seems to make the core machinery alot more
> complicated.

Here is how we "see the world":

There are subjects (anything you want to talk about). Subjects are
represented as topics (the topics are the nodes of the graph that is
'produced' from a topic map). Topics have properties that say what
the subject of the topic is.

Topic Maps are not tied to the Web or URIs conceptually, but it is
the most known application of them at the moment. So, when applying topic
maps to the Web world, there are two properties that handle the use
of URIs: SubjectIndicators and SubjectAddress.

The value (if any) of the SubjectAddress property is a URI and if a given
topic exhibits a value for this property, then the topic is a surrogate
for the subject that is the resource (in the sense of Web page, never
abstract concept). 

The value (if any) of the SubjectIndicators property is a list of URIs,
and each Web resource (again: in the sense of Web page) addressed by 
the URIs is called a subject indicator (or "subject indicating resource")
for the subject that the topic represents. 

So, the core machinery is actually as simple as "nodes with properties
the 'say' what the node represents".

This is not the whole story of course, but I hope you get the idea.


Jan Algermissen                           http://www.topicmapping.com
Consultant & Programmer	                  http://www.gooseworks.org
Received on Tuesday, 1 April 2003 05:50:58 UTC

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