> From [log in to unmask] Thu Jan 16 15:26 MET 2003
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> Thread-Topic: rdfs:isDefinedBy revisited
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> Date: Thu, 16 Jan 2003 16:26:09 +0200
> From: Patrick Stickler <[log in to unmask]>
> Subject: Re: rdfs:isDefinedBy revisited
> To: [log in to unmask]
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> > -----Original Message-----
> > From: ext Jon Hanna [mailto:[log in to unmask]]
> > Sent: 16 January, 2003 15:23
> > To: [log in to unmask]
> > Subject: Re: rdfs:isDefinedBy revisited
> >
> >
> > > I don't think it is well defined in any context. And I think
> > > that the issue of what is a valid representation of a resource
> > > or that one never can actually access the resource itself is
> > > the very crux of the apparent friction between the Web and
> > > the Semantic Web.
> >
> > !
> > Firstly I don't see what this has to do with the semantic web
> > (apart from it
> > being part of the web).
>
> Because most folks think that a URI denotes what they get
> when they dereference it, and that is not necessarily what
> it actually denotes to a reasoning engine. Yet if they
> start making statements about what they got, using the
> name of "where" they got it, then they introduce noise
> into the SW.
>
> If I have a URI that denotes the city of Paris, and someone
> dereferences it and gets a representation that is a photo
> of Paris, and they say "Paris is out of focus" when they
> really meant to say, "The photographic representation of Paris
> I got is out of focus" then the SW becomes a repository for
> garbage, not knowledge.
I don't quite get what you want to say.
Suppose i retrieve a picture from a URL1, which according to my
previous knowledge shows a cat and you assert in some
semantic web URL1 --rdf:type--> "dog"
Can you tell what conclusion i should make in your semantic web?
Cheers,
rs
>
> So clarifying what URIs denote and the distinction between
> resources and representations and the URIs used to denote
> resources versus representations is paramount to making the
> SW work as a layer upon the Web.
>
> > Secondly how can possibly you access anything other than a
> > representation?
> > The concept of resource doesn't rule out the possibility that
> > a resource may
> > be one and the same as what is accessed (a clear example
> > being downloaded
> > software obtained from a uri designed purely to be were the
> > software lives).
> > It just recognises that this isn't always the case. It's a
> > recognition of
> > the way things are, not a statement about how things should be.
> >
> > I most likely get a different response to deferencing
> > "http://www.google.com/" than you. (Unless you are also in
> > Ireland). That
> > doesn't change the fact that <http://www.google.com/> is resource.
>
> For many use cases, content negotiation is a good thing. But what if
> I need a precise copy, bit for bit, of a digital resource? Or if I
> need to make a particular statement about a particular resource
> (not representation) such as a checksum or digital signature?
>
> The standard conneg reply is that you can ask for what you want, but
> this is not anywhere nearly precise enough for many, many use
> cases since there is no standard saying exactly *how* you can
> say what you want (MIME type doesn't cut it) and there is no
> official concept of a canonical or platonic representation which
> is *the* representation unless you say otherwise, and how a
> server tells a client that it has returned (or not returned) such
> a canonical representation.
>
> For digital resources, that canonical representation would be a
> bit-for-bit copy (not a transformation, not a summary, etc).
>
> For non-digital or otherwise abstract resources, the owner of
> the URI would be able to specify which is the canonical representation.
>
> But this is, I agree, a completely separate issue that doesn't need
> to live on this particular discussion list...
>
> Cheers,
>
> Patrick
>
>
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