Kevin Richards wrote:
This mention of owl:sameAs reminds me of the mention of the "sameAs issue", at
ISWC, that has developed in the semantic web arena.
I can imagine what this issue is, but am not 100% sure, so can anyone explain
this issue to me?
I remember there is a discussion on one of the W3C's mailing list about
the ambiguity of "owl:sameAs" but couldn't remember where it is. But I
can offer my own explanation.
Its cause is a very fundamental one because the current URI
specification is, in fact, syntactically incomplete. With current URI
spec, the referential realm of URI is anything but URI. (Of course, I
can mint another URI to denote another instance of a URI class, but then
there needs to be a standard way to find this information).
Thus, if a URI denotes a URI, the semantics of "a owl:sameAs b" would
mean that "a" is simply an syntactic alias of "b" and nothing-else.
But if a URI denotes a non-URI resource, "a owl:sameAs b" would imply
that a semantic alias. That is: "a" is an syntactic alias of "b" PLUS
a's and b's representations collectively describe the meaning of "a/b".
To put it plainly, the second semantics implies an owl:import but the
first one does not because the representation of a URI is literally
itself but the representation of a resource requires dereference. I
think, with the current URI specification, the owl:sameAs is for the
second semantics. In this case, it is not as cheap as people think that
minting a URI first and later binding it with others using owl:sameAs.
If a's representation is not logically consistent with b's, then the
owl:sameAs leads to a null model.
What makes the issue complicated, however, is that the ambiguity of
owl:sameAs is not with the problem of OWL but that of URI. The issue
also touched upon our conceptualization of URI, resource,
representation, information/document, and meaning. I have discussed
this issue quite extensively in a manuscript that I have submitted to
WWW2009. As a pending manuscript, I don't think that it is appropriate
to post it here. But if anyone is interest in reading it, send me an email.
Xiaoshu
Thanks
Kevin Richards
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Harry Halpin
Sent: Friday, 28 November 2008 2:05 a.m.
To: Richard Cyganiak
Cc: John Graybeal; public-lod@w3.org; Semantic Web
Subject: Re: Dataset vocabularies vs. interchange vocabularies
On Thu, 27 Nov 2008, Richard Cyganiak wrote:
On 26 Nov 2008, at 21:53, John Graybeal wrote:
<snip>
would you agree that duplicating a massive set of URIs for 'local technical
simplification' is a bad practice? (In which case, is the question just a
matter of scale?)
You are asking me if 'local technical simplification' is a good reason or a
bad reason for duplicating URIs? Uh, I guess it depends...
My point was this: The key benefits of URI re-use can also be obtained by
minting your own URIs and linking them to existing URIs via adequate RDF
properties. And that practice can have additional practical/implementation
benefits (and costs). Hence, consider both options; there's no reason to
knee-jerk against creating new identifiers.
I agree in theory with Richard, but in practice with John. The key
benefits of URI re-use can only be gained by using multiple URIs if we
have "adequate URI properties" (i.e. owl:sameAs?) and given an adequate
reasoning system that can identify the same URIs in any data set -
including large ones - where we want to merge data using these "inferred
to be the same" URIs.
To my knowldge, we have neither adequate URI properties or working
reasoning services, at least for the end-user. Now perhaps this will
change, but if not, why not re-use URIs?
If we do have adequate URI properties besides the infamous owl:sameAs,
please point me to them. And while at ISWC there was clearly lots of work
on large-scale identity management trying to discover URI equivalences via
inference, I'm not sure how well that works right now.
Furthermore, there's the question of what URI to use in the output if one
is identifying URI's to be the same and one wants to re-use the merged data.
-harry
> Best,
Richard
John
--------------
John Graybeal <mailto:[EMAIL PROTECTED]> -- 831-775-1956
Monterey Bay Aquarium Research Institute
Marine Metadata Interoperability Project: http://marinemetadata.org
--
--harry
Harry Halpin
Informatics, University of Edinburgh
http://www.ibiblio.org/hhalpin
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