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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. 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