W3C home > Mailing lists > Public > public-owl-wg@w3.org > October 2007

Re: comments on RDF mapping

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Mon, 29 Oct 2007 18:00:08 +0000
Message-ID: <47261FA8.90509@hpl.hp.com>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
CC: Boris Motik <boris.motik@comlab.ox.ac.uk>, public-owl-wg@w3.org


I think the best way to address punning is by stating the requirement 
and looking at whether:

a) this requirement is a requirement, and how widespread
b) whether punning meets this requirement

The only articualtion of the requirement that I am familiar with is:

http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.19-Classes-as-instances


During the earlier group I felt that it was understood that the 
requirement was not just that you could use the same name for a class as 
for an instance, but that some logical consequences would follow.

for example
http://www.w3.org/TR/owl-test/byFunction#sameAs-001

This is an OWL 1.0 Full entailment, which (perhaps with minor syntactic 
change) would become an OWL 1.1 DL non-entailment (if I have understood 
punning semantics correctly).

This seems like a divergence away from OWL 1.0 balance between Full and 
DL, and also a divergence away from what I believe the requirement of 
classes as instances is. If two items are the same instance, then they 
are necessarily the same class.

The tests that I think express the punning issue are:


<a> owl:sameAs <b>

entails

<a> owl:equivalentClass <b>


and


<a> owl:sameAs <b>

entails

<a> owl:equivalentProperty <b>


I currently believe that the member submission OWL 1.1 semantics has 
these both as non-entailments, and that a requirements doc for the use 
case of using an instance URI as a class URI or an instance URI as a 
property URI would have these entailments as holding.

(Obviously it is possible to give a post hoc rationale in which these 
entailments are unimportant - it is easier to tell whether or not a 
design meets a requirement if the requirement is written down, before 
the design is)

Since the OWL 1.0 design solves this problem, in the manner given by

http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.19-Classes-as-instances
[[
Part of OWL Full.
]]
(and syntactically excluded from OWL DL)

I personally see a variation in which this becomes

"Part of OWL Full; syntactically permitted in OWL DL, but with weaker 
semantics."

as a backward step

Jeremy





Alan Ruttenberg wrote:
> Hi Jeremy,
> 
> My understanding is that the intention is not to provide a way to get 
> around the univocity of a URI. Rather, some aspects of making that work 
> are not currently known to be decidable, so a compromise is offered  
> insofar as some entailments that would be theoretically desired are 
> skipped, in order to make progress towards a shared goal.
> 
> I wonder whether we can make some fixes to address cases such as the one 
> you point out, particularly when there is no impact on decidability. So 
> perhaps we could consider, in this case, abandoning the distinction 
> between subObjectPropertyOf and subDataPropertyOf so that a subProperty 
> assertion applies to both kinds.
> 
> There will still be an issue with property chains. But I wonder what you 
> think about the general strategy: Making it clear in the documentation 
> that we discourage use of punning to get around univocity, that current 
> behavior that allows this may disappear in future versions of OWL, and 
> patching, to the extent that is feasible without new theoretical work, 
> the current spec in the way that I suggest above.
> 
> As a meta point, could we stay away from statements of the sort : "i.e. 
> punning is an unhelpful idea."? I don't think it is helpful, as there 
> are clearly situations where other people do think it is helpful. Let's 
> instead focus on making things work as best we can.
> 
> -Alan
> 
> 
Received on Monday, 29 October 2007 18:01:02 GMT

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