- From: Pat Hayes <phayes@ihmc.us>
- Date: Sat, 14 Dec 2013 03:14:28 -0800
- To: David Booth <david@dbooth.org>
- Cc: Richard Cyganiak <richard@cyganiak.de>, Guus Schreiber <guus.schreiber@vu.nl>, public-rdf-comments <public-rdf-comments@w3.org>
Quick comments inserted in-line. On Dec 13, 2013, at 3:10 PM, David Booth <david@dbooth.org> wrote: > Hi Richard, > > On 12/13/2013 04:51 PM, Richard Cyganiak wrote: >> Hi David, >> >> On 13 Dec 2013, at 19:23, David Booth <david@dbooth.org> wrote: >>> 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, PLEASE, PLEASE don’t do this. >> >> It is true that an IRI can denote different things in different >> interpretations. True, but utterly irrelevant to this issue. >> But we are talking here about a brief and >> *informative* introduction to semantic web architecture of two pages. >> It cannot, and should not, get into the business of explaining >> interpretations and possible worlds. > > I agree with that. But that doesn't mean that it needs to be misleading and wrong. A balance is possible. > >> >> So we are concerned here with only one possible world, the one we >> live in. > > I do not agree. I do not believe that that is in fact how we use RDF. It is what underlies all use of RDF as 'linked data'. > >> In this particular possible world, an IRI denotes the same >> thing wherever it occurs. For the vast majority of readers, this is >> all they ever need to know. > > I do not agree. I think we need to alert them to the fact that, although this is the *goal* and the *intent*, it is *not* the reality. And they need to watch out for this when merging graphs, or they're going to run into trouble and disappointment. Juat as with uniquness of IRI identification on the broader Web, it is both an important architectural principle, and largely true, but sophisticated users need to know that it can be false in practice, at times. >> Now, you are right, RDF Semantics introduces the notion of >> interpretations, and an IRI can denote different resources in >> different interpretations. But this denotation of different resources >> is not even a *feature*. It is simply part of the formalism that >> happens to be used to define what entailments are correct. Had the >> semantics been formally defined using inference rules rather than >> model theory, then the phrase you quote would be absolutely correct. > > I can't comment on that, as I don't know exactly how it would look. > >> >> In summary, David, you give us two alternatives. >> >> a) Either we need to introduce a brief informative account of the way >> IRIs work on the semantic web with caveats about multiple possible >> worlds. b) Or we can’t tell people that an IRI that occurs twice >> should always be taken as identifying the same thing. > > But those are not the only two options. I think we can easily say that different occurrences of an IRI are *intended* to denote the same thing. That would indeed be possible, but... > That would prevent the statement from being *wrong*. And we can give a pointer to a more complete explanation, perhaps saying that if an IRI either accidentally or otherwise was used to denote different resources in two source graphs, then ... we cannot say or point to that, because it is meaningless. The notion of "denoting in a graph" is incoherent. > this may cause problems when merging those graphs, because RDF *assumes* that the IRI denotes the same resource everywhere it appears in the merged graph. I think it is important to alert readers to this real life difficulty with graph merging, rather than leading them down a garden path, only to be confused and disappointed when graphs do *not* merge as expected. Graphs always merge. What may be unexpected is when this produces inconsistencies. > My original comment included a very modest suggestion for fixing this text: > http://lists.w3.org/Archives/Public/public-rdf-comments/2013Oct/0008.html > [[ > "IRIs are *intended* to have global scope: Two different > appearances of an IRI are *intended* to denote the same resource." The following: > (However, the RDF Semantics explains how an IRI may denote > different resources in different interpretations.) is highly misleading and should not be used. It suggests some relevance to the issue which it does not in fact have. Pat > ]] > > I am sure that text could be improved -- and my suggestion above would improve it to avoid mentioning interpretations altogether -- but the point is that this text does not need to be complicated or too highly technical to avoid being misleading and wrong. > >> >> Either option is harmful to the intended audience of RDF Concepts. >> All in the name of being *technically* correct. > > No, not only in the name of being *technically* correct, but also in the name of not being *misleading*. > > David > >> >> Again, it’s a *non-normative* section, it’s the *introduction*, it’s >> intended to be understandable by people who will never look at RDF >> Semantics, and the sentence is even true within any given single >> interpretation! >> >> Best, Richard ------------------------------------------------------------ IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 mobile (preferred) phayes@ihmc.us http://www.ihmc.us/users/phayes
Received on Saturday, 14 December 2013 11:14:57 UTC