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Re: Terminology Question concerning Web Architecture and Linked Data

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 31 Jul 2007 10:09:49 -0500
Message-Id: <p06230910c2d3eca74003@[10.100.0.67]>
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
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Received on Tuesday, 31 July 2007 15:10:21 GMT

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