- From: David Booth <david@dbooth.org>
- Date: Fri, 13 Dec 2013 14:23:20 -0500
- To: Guus Schreiber <guus.schreiber@vu.nl>
- CC: public-rdf-comments <public-rdf-comments@w3.org>
Hi Guus, I'm sorry, I was holding off on replying to that previous email, pending a long conversation with Pat Hayes, in which I hoped to reach a common view on this issue. But apparently I have failed. :( No, I cannot live with this. The current draft of the RDF Concepts says: "IRIs have global scope: Two different appearances of an IRI denote the same resource. and that is simply misleading and false, as explained here: http://lists.w3.org/Archives/Public/public-rdf-comments/2013Dec/0073.html Please let me know what I can do as a next step toward resolving this satisfactorily. Or, alternately, let me know what I should do to present this as a formal objection. Thanks, David On 12/05/2013 06:04 AM, Guus Schreiber wrote: > David, > > As far as we can see we did not receive a reply from you on this > response from the RDF WG on ISSUE-148. Could you please indicate whether > you can live with this? > > Best, > Guus > > > On 06-10-13 20:59, Guus Schreiber wrote: >> David, >> >> The Working Group thanks again you for your concerns on this important >> aspect of the RDF recommendations, which have been tracked as ISSUE 148. >> >> The wording that you mention "IRIs have global scope: Two different >> appearances of an IRI denote the same resource." is part of the >> introduction to IRIs in RDF. Even though this introduction is informal >> and non-normative and has to be short, it is in fact very important as >> it sets the tone for the rest of the discussion on IRIs in both Concepts >> and Semantics. The wording is trying bring forward the idea that every >> occurrence of an IRI is the *same* identifier, i.e., IRIs are global >> identifiers. >> >> The first part of the wording says this explicitly, but it was felt that >> some amplification of the point was desirable hence the second part of >> the wording, emphasizing that different occurrences of IRIs are treated >> the same in any formal context. Your concerns have illustrated that >> this part is not achieving its desired purpose. >> >> The working group has two proposals that might address your concerns: >> 1/ Remove the second part, and make the first part carry the entire load. >> 2/ Replace the second part with "Two different appearances of an IRI >> identify the same resource.", which appeals to the non-formal notion of >> identification instead of the formal notion of denotation. >> >> Could you please respond to public-rdf-comments@w3.org as to whether >> either of these changes is satisfactory, and whether you have any >> preferences between them? >> >> Best, >> Guus Schreiber >> co-chair RDF WG >> >> On 02-10-13 13:23, Guus Schreiber wrote: >>> Dear David, >>> >>> Thanks for your comment. We have raised an issue for tracking your >>> comment [1]. We will get back to you on this. >>> >>> Best, >>> Guus, on behalf of the RDF WG >>> >>> [1] https://www.w3.org/2011/rdf-wg/track/issues/148 >>> >>> On 02-10-13 07:05, David Booth wrote: >>>> In https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html >>>> I see this statement: >>>> >>>> "IRIs have global scope: Two different appearances of an IRI >>>> denote the same resource." >>>> >>>> This is wrong. If it were true then there could never be a URI >>>> Collision >>>> http://www.w3.org/TR/webarch/#URI-collision >>>> and there would be no point in the AWWW discussing it or admonishing >>>> against it. >>>> >>>> An IRI can and often does denote different resources in different >>>> *interpretations*. And this, in practice, means that an IRI often >>>> denotes different resources in different *graphs*, because any graph >>>> has >>>> a set of satisfying interpretations, and different graphs may have >>>> different sets of satisfying interpretations. For example, suppose >>>> graphs g1 and g2 have sets of satisfying interpretations s1 and s2, >>>> respectively, and those sets may be disjoint. Then colloquially (and >>>> technically) we can say that an IRI may map to one resource in g1 >>>> (i.e., >>>> in some interpretation in s1) and a different resource in g2 (i.e., in >>>> some interpretation in s2). >>>> >>>> This requires thinking about graphs in terms of sets of satisfying >>>> interpretations -- an important and valid perspective -- rather than >>>> assuming that one looks at them only through the lens of a single >>>> interpretation. >>>> >>>> As a simple example of how a URI can denote different things in >>>> different graphs, suppose Alice sends this graph G1 from her smart >>>> phone >>>> to her home computer to turn *on* her porch light (assuming the usual >>>> URI prefix definitions): >>>> >>>> G1: { @prefix db: <http://dbooth.org/> >>>> ex:alicePorchLight rdf:value db:x . >>>> db:x owl:sameAs ex:on . >>>> ex:on owl:differentFrom ex:off . } >>>> >>>> and her light turns on. >>>> >>>> In contrast, Bob sends this graph G2 from his smart phone to his home >>>> computer to turn *off* his oven: >>>> >>>> G2: { ex:bobOven rdf:value db:x . >>>> db:x owl:sameAs ex:off . >>>> ex:on owl:differentFrom ex:off . } >>>> >>>> and his oven turns off. >>>> >>>> It is perfectly reasonable and natural to ask "What resource does db:x >>>> denote in G1?", and it is reasonable and natural to ask the same of G2. >>>> The RDF Semantics (along with OWL) tells us that in G1 db:x denotes >>>> whatever ex:on denotes, whereas in G2 db:x denotes whatever ex:off >>>> denotes. That is useful! Furthermore, the semantics tells us that if >>>> we merge those graphs then we have a contradiction -- there are no >>>> satisfying interpretations for the merge -- and that is useful to know >>>> also, because it means that Alice and Bob's graphs **cannot be used >>>> together**. >>>> >>>> Furthermore, the RDF Semantics notion of an interpretation maps well to >>>> real life applications: in effect, an application chooses a particular >>>> interpretation when it processes RDF data. This is a very useful >>>> aspect >>>> of the model theoretic style of the semantics. In this example, >>>> Alice's >>>> home control app interpreted db:x to denote "on" and Bob's home control >>>> app interpreted it to denote "off". And *both* were correct (in >>>> isolation): they both did The Right Thing. >>>> >>>> In short, I think the above statement needs to be qualified somehow, >>>> such as: >>>> >>>> "IRIs are *intended* to have global scope: Two different >>>> appearances of an IRI are *intended* to denote the same resource." >>>> (However, the RDF Semantics explains how an IRI may denote >>>> different resources in different interpretations.) >>>> >>>> David >>>> >>> > > >
Received on Friday, 13 December 2013 19:23:49 UTC