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> From [log in to unmask] Thu Jan 16 11:38 MET 2003 > X-RAL-MFrom: <[log in to unmask]> > X-RAL-Connect: <pat.bath.ac.uk [138.38.32.2]> > MIME-Version: 1.0 > Content-Transfer-Encoding: 7bit > X-Priority: 3 (Normal) > X-MSMail-Priority: Normal > X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 > Importance: Normal > Date: Thu, 16 Jan 2003 10:40:29 -0000 > From: Pete Johnston <[log in to unmask]> > Subject: Re: rdfs:isDefinedBy revisited > To: [log in to unmask] > X-Spam-Status: No, hits=-0.8 required=5.0 > tests=IN_REP_TO,QUOTED_EMAIL_TEXT,SPAM_PHRASE_00_01 > version=2.43 > > Patrick, > > Thanks for this. Yes, I remember you made a similar point in the thread > here back in May/June (but yes, it's worth reiterating, I think). > > The problem you describe (and address with your x:Vocabulary and > x:RDFSchema classes and x:term property) is (I think) pretty much > _exactly_ what motivated my initial ruminations on this topic, and why I > embarked on this hair-splitting to establish exactly what are the > resources we are talking about. > > i.e. I wanted to express the relationships between terms (in my case I > was specifically interested in the subset that DC calls elements i.e. > RDF properties) and "functional" sets/aggregates of those terms (element > sets, vocabularies, term sets, whatever we call them), where there was > no _necessary_ coincidence between the set of names of elements in one > "element set" and the set of names "in" an XML namespace. And an RDF/XML > representation was a different resource again. Yes, often there is a > one-to-one mapping but it's not necessarily so. > > So I've ended up coining classes "Schema", ElementSet" and a property > "isElementOf". It just continued to niggle me that I was introducing > these "local" semantics that I should avoid if possible, but I think > your example below clarifies to me that it is useful/necessary. The classes "Schema" "ElementSet" "isElementOf" you still need to declare in some formal fashion - an you will need a namespace for those and representations in whatever Schema languages .... It seems to me you just entered another round. > > And as you say, in this application, I absolutely should not deploy a > URI which is already in use as an XML namespace name as the identifier > of one of these functional aggregates (which was a mistake I made > earlier!) Why not? You're using the same notation (URI) for instance, when doing content negotiation for language. You definitely in general will receive objects a "diff" will mark as different for "en-GB" and "en-US" - Nevertheless they are both retrievable from the same URI. Cheers, rs > Thanks again - that was very helpful. > > Pete > > > -----Original Message----- > > From: DCMI Architecture Group > > [mailto:[log in to unmask]] On Behalf Of Patrick Stickler > > Sent: 16 January 2003 09:18 > > To: [log in to unmask] > > Subject: Re: rdfs:isDefinedBy revisited > > > > > > > -----Original Message----- > > > From: ext Pete Johnston [mailto:[log in to unmask]] > > > Sent: 15 January, 2003 16:01 > > > To: [log in to unmask] > > > Subject: Re: rdfs:isDefinedBy revisited > > > > > > > > > ... I definitely do want to distinguish > > > > > > - a set of terms or names (1 or 2) identified by a URI e.g. > > > http://purl.org/dc/elements/1.1/ > > > > Fair enough. This would equate to a functional vocabulary, as > > outlined below, but I'd use a different URI from that used as > > the XML namespace URI. > > > > > - a particular representation of that set of terms (e.g. an RDF/XML > > > document) which happens to be Web retrievable using that > > same URI (3) > > > > If the URI denotes a vocabulary, then an RDF/XML > > representation of the definition of that vocabulary would be > > appropriate. > > > > -- > > > > This may be obvious and I probably don't need to mention it, > > but the object of rdfs:isDefinedBy need not be the thing > > denoted by the XML namespace URI. In fact, if one has several > > different schemas (XML Schema, RDFS, RELAXNG, OWL, XTM, etc.) > > not to mention multiple instances of a given encoding (e.g. > > separate RDFS instances defining labels and descriptions for > > each language) which all provide definition of a term, then > > each may be identified by an rdfs:isDefinedBy statement. > > > > I.e., there is no requirement for the pattern > > > > XXX:term rdfs:isDefinedBy XXX > > > > and IMO it should be avoided. > > > > A given functional vocabulary, such as DC, need not be > > constrained to terms grounded in only one namespace, and the > > resource defining that vocabulary need not equate to the > > resource(s) defining the individual terms. There can thus be > > multiple functional vocabularies which share common terms and > > the definition of the vocabulary is not dictated by the > > definition of the terms. A good example of this is PRISM, > > which is a functional vocabulary which includes terms from > > other functional vocabularies (e.g. DC) as well as defining > > terms of its own. And of course, the identity of a given vocabulary > > is not the same as a particular namespace (and in the case > > of vocabularies with terms from multiple namespaces, cannot > > be the same), and hence vocabularies should have a distinct > > URI from any XML namespaces. > > > > IMO a vocabulary equates to a DCMI namespace. > > > > Thus, the formal definition of a vocabulary such as DC or > > PRISM could be organized thus (this is how we do it at Nokia): > > > > RDF instance a:S > > [ > > a:S rdf:type x:RDFSchema . > > a:V rdf:type x:Vocabulary . > > a:V x:term g:t1 . > > a:V x:term g:t2 . > > a:V x:vocabulary b:V . > > a:V rdfs:isDefinedBy a:S . > > ] > > > > RDF instance g:S > > [ > > g:S rdf:type x:RDFSchema . > > g:t1 rdf:type rdf:Property . > > g:t1 rdfs:label "Term G1" . > > g:t1 rdfs:isDefinedBy g:S . > > g:t2 rdf:type rdf:Property . > > g:t2 rdfs:label "Term G2" . > > g:t2 rdfs:isDefinedBy g:S . > > ] > > > > RDF instance b:S > > [ > > b:S rdf:type x:RDFSchema . > > b:V rdf:type x:Vocabulary . > > b:V x:term h:t1 . > > b:V x:term k:t1 . > > h:t1 rdf:type rdf:Property . > > h:t1 rdfs:label "Term H1" . > > h:t1 rdfs:isDefinedBy b:S . > > k:t1 rdf:type rdf:Property . > > k:t1 rdfs:label "Term K1" . > > k:t1 rdfs:isDefinedBy b:S . > > ] > > > > Here we have 6 different XML namespaces, two vocabularies, > > and four terms, all defined in three RDF resources. Each > > vocabulary defines the terms and/or subvocabularies it > > includes. The first > > vocabulary subsumes all the terms in the second vocabulary. > > Insofar as the definition of the vocabularies is concerned, > > the XML namespaces used by the individual terms is > > irrelevant. The RDF resource g:S defines terms that are all > > grounded in the same vocabulary. The RDF resource b:S not > > only defines terms grounded in different namespaces but a > > vocabulary as > > well. > > > > So, hopefully it is clear that there is no fixed relation > > between vocabularies, XML namespaces and schemas, and in fact > > it is far more flexible and scalable to avoid any ambiguity > > in this regard by presuming that the XML namespace denotes > > any particular schema or vocabulary. > > > > XML namespace != vocabulary != model != schema instance > > > > Just thought I'd reassert those points... > > > > Cheers, > > > > Patrick > > > >