- From: Pat Hayes <phayes@ihmc.us>
- Date: Mon, 30 Jul 2007 14:49:46 -0500
- To: Hugh Glaser <hg@ecs.soton.ac.uk>
- Cc: Tim Berners-Lee <timbl@w3.org>, Chris Bizer <chris@bizer.de>, <www-tag@w3.org>, <semantic-web@w3.org>, Linking Open Data <linking-open-data@simile.mit.edu>
>I am trying hard to keep up (I suspect like many), and was hoping someone >would address a concern I have; forgive me if I missed it somewhere in the >discussion. >I have hung this off this message from Tim, which seems the most relevant. >And congratulations on the Linked Data Tutorial - a really useful document. > >So here we go: > >On 25/7/07 14:35, "Tim Berners-Lee" <timbl@w3.org> wrote: > >> >> (Going back to the original question, as it is much simpler than much >> which follows!) >> >> On 2007-07 -07, at 08:43, Chris Bizer wrote: >> >> >>> Question 3: Depending on the answer to question 1, is it correct to >>> use owl:sameAs [6] to state that http://www.w3.org/People/Berners- >>> Lee/card#i and http://dbpedia.org/resource/Tim_Berners-Lee refer to >>> the same thing as it is done in Tim's profile. >> >> Yes. >> >So Tim absolutely right. >This is an entirely logical thing to say. >These two NIRs (Non-Information Resources) should be considered the same. (Aside) I wish folk would not say 'two' when there is only one. Two NIRs should never be considered the same: rather, two names may refer to the same, single, NIR. >But it is important to consider how this statement will be used, and worry >whether there may be unexpected consequences. >As we now know, the URIs should be resolvable, and so interesting Semantic >Web applications will use the URI to get the Description (or whatever we >call it), probably going via a 303. >So my SW app will get the RDF of them both, and add it to my triplestore, >along with all the other linked data. > >Tim, as often, is a good example. >Consider the places Tim works (W3C, MIT, Southampton, I guess). >It is likely that each will publish RDF about him, hopefully using an agreed >ontology (one day!). >Now comes the rub. >If you put all this in one triplestore, with the owl:sameAs assertions, then >it will not be possible to distinguish where facts came from, or rather >which facts are associated with which others. Whoa, careful. It will probably will be >>possible<< to distinguish this, in fact. It might be that unwanted consequences are entailed by the combination of the various RDF graphs and the sameAs, but a careful querying process should be able to determine which of the various triples are present and even whether they are linked. One simple way is to query under sub-OWL entailment, for example, which can be little more than a direct syntactic matching process (see SPARQL). >Perhaps 3 job titles, 3 telephone numbers and 3 institution addresses will >be returned from the appropriate SPARQL queries, and there will be no >(legal) way of working out which corresponds to which. That would be a symptom of poor RDF/OWL usage, though. Assertions in RDF are not supposed to be local-context-sensitive in the way you seem to be assuming. So for example it would be a mistake to simply assert, in the w3c page, that Tim's status WAS Director. It ought to say that a relationship holds between him and the entity he is the Director of, i.e. the W3C; so that this stays true even when it is moved somewhere else on the Web. In fact, I suggest that as a basic, fundamental principle of any 'web logic' is that assertions in it should have the same meaning wherever they occur on the Web (see for example http://www.ihmc.us:16080/users/phayes/IKL/GUIDE/GUIDE.html#LogicForInt) >So I can infer that the person http://www.w3.org/People/Berners-Lee/card#i >is a Professor at MIT, or a Senior Research Scientist at W3C, or Director at >Southampton, none of which we consider true. >(Of course, this was the intention of the sameAs assertion.) > >I suggest that this is a bad state of affairs It would be, yes, but it should not arise if the RDF is written properly. >, and applies to any NIR, not >just people. It applies to any R, I or NI. Its really nothing to do with the nature of the thing named. Pat Hayes -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 30 July 2007 19:50:02 UTC