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RE: URI Declarations [Usage scenarios 4 and 5]

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 3 Mar 2008 11:02:46 -0600
Message-Id: <p06230905c3f1dba96310@[10.100.0.20]>
To: "Booth, David (HP Software - Boston)" <dbooth@hp.com>
Cc: "ashok.malhotra@oracle.com" <ashok.malhotra@oracle.com>, John Cowan <cowan@ccil.org>, "www-tag@w3.org" <www-tag@w3.org>

At 12:39 AM +0000 3/3/08, Booth, David (HP Software - Boston) wrote:
>  > From: Pat Hayes [mailto:phayes@ihmc.us]
>>  [ . . . ]
>>  BUt take this (actual) example: I recently found
>>  an entry on a site which listed interesting facts
>>  about various numbers:
>>
>>  30.48  ....  By convention, the number of inches in a foot.
>>
>>  Hmm. Seemed to me like a typo (which it was, of
>>  course.) But following the logic used by David,
>>  what I should have done was assume that the site
>>  didn't mean what it seemed to mean by the numeral
>>  "30.48", and in fact it meant that to denote 12.
>>  Or maybe, it meant "foot" to denote a yard, or a
>>  meter; or, maybe, that it meant "inch" to denote
>>  centimeter. None of which seem like sensible
>>  strategies to me.
>
>No, that's not the logic I'm suggesting.  Let me make your example 
>more concrete to better illustrate what I'm suggesting.
>
>SCENARIO 4: Gary publishes a lumber ontology at 
>http://gary.example/lumber.  The ontology includes the concept of a 
>standard 8-foot "2x4", which is denoted by the URI 
>http://gary.example/lumber#2x4x8.  Pat is writing a set of 
>assertions to describe the house he plans to build, and he is 
>interested in Gary's #2x4x8 URI, but during testing he notices that 
>Gary's ontology (erroneously) asserts that "30.49 inches = 1 foot". 
>For perhaps obvious reasons, Pat does NOT wish to accept that 
>assertion.
>
>Question: Should Pat use http://gary.example/lumber#2x4x8 to denote 
>a standard 8-foot "2x4" anyway?
>
>My answer: No.

OK, we disagree. I think I should contact Gary and point out to him 
his error, and use his URI when I do so. If I have no way to contact 
him, I should publish an ontology using his URI but correcting his 
error, and maybe (if possible) indicate explicitly that this ontology 
is a correction to his ontology, which is (in my opinion, of course) 
deprecated. Maybe I can include an annotation property to a comment 
indicating the reason (for humans to read). The world now has two 
versions of an ontology, and its up to others which they want to use.

>  Pat should either find a different ontology to use, or mint a new 
>URI and indicate its relationship to Gary's URI.

The relationship would be owl:sameAs, so what's the point of minting 
a new URI? All the semantic consequence, for good or ill, follow in 
the same way.

>For example, Pat could make a copy of Gary's ontology (with Gary's 
>permission, of course), delete the offending assertion, change every 
>occurrence of "http://gary.example/lumber" to 
>"http://pat.example/lumber" and publish the new ontology at 
>http://pat.example/lumber.    The assertions for his house should 
>then use http://pat.example/lumber#2x4x8 instead of 
>http://gary.example/lumber#2x4x8.

WHY should I do this? What is the PURPOSE of this recommendation? 
What utility does it serve?

>
>SCENARIO 5: Helen is writing some assertions about the color of 
>concrete, and is also interested in using a URI from Gary's ontology 
>to denote concrete: http://gary.example/lumber#concrete.  Helen's 
>application makes no use whatsoever of linear dimensions, so 
>although she is aware of the erroneous assertion that Pat 
>discovered, it does not interfere with her application.
>
>Question: Should Helen use http://gary.example/lumber#concrete to 
>make assertions about concrete?
>
>My answer: She may, but she probably shouldn't, because it would 
>severely restrict the reuse of her assertions.

My answer: The use of a URI does not restrict re-use of assertions 
involving that URI in any way whatsoever. There is no mechanism in 
Web architecture available to enforce such a 'restriction', any more 
than there is to architecturally restrict what use is made of a Web 
page once it is published.

>  Helen's assertions presume that the "core assertions" in Gary's URI 
>declaration at http://gary.example/lumber have been accepted -- 
>including the erroneous assertion that "30.49 inches = 1 foot".  So 
>if an application using Helen's assertions makes use of linear 
>dimensions, and it recursively pulls in Gary's ontology, then Gary's 
>erroneous assertion about the number of inches to a foot is likely 
>to cause havoc.

Well, its likely to produce detectable inconsistencies. What one does 
when such a thing is found, is up to the application. It needn't be 
'havoc'. A conservative strategy would be to post an error condition 
and hope that a competent human being will sort things out.

>  If the application is lucky enough to have other information 
>indicating that "12 inches = 1 foot" then it may detect a logical 
>inconsistency.  If it is unlucky, it may silently produce absurd 
>conclusions, such as "David Booth is over 180 inches tall".
>
>SCENARIO 6: Helen is lazy and publishes her color assertions at 
>http://helen.example/colors anyway, using 
>http://gary.example/lumber#concrete to denote concrete.  Ian finds 
>Helen's assertions and wishes to use them, but he notices that 
>Gary's ontology at http://gary.example/lumber erroneously asserts 
>that "30.49 inches = 1 foot", and Ian's application cannot withstand 
>that erroneous assertion.  Ian is aware that Pat has published an 
>ontology at http://pat.example/lumber that is equivalent to Gary's 
>ontology except that it does not contain this erroneous assertion.
>
>Question: What should Ian do?
>
>My answer: Ian should effectively rewrite Helen's assertions to use 
>http://pat.example/lumber#concrete instead of 
>http://gary.example/lumber#concrete throughout.

My recommendation: he should leave his ontology alone, but have it 
import the corrected version rather than Gary's, thereby endorsing 
the truth of a different set of assumptions. There is no need to get 
involved with changing the URIs or elaborate mechanisms for textual 
substitution, since the disagreement is not about reference, but 
about the facts of the matter. Both Gary's and my ontologies are 
intended to refer to the same entities, but we differ on the facts. 
It is therefore perfectly correct to use the same URI in both 
ontologies, even though the ontologies are mutually inconsistent.

Pat

>He can either do this by modifying a copy of Helen's assertions, or 
>by reference, using special expressions to indicate proper URI 
>substitution in Helen's graph.  (I intend to describe this further at
>http://dbooth.org/2007/splitting/#urisub .)
>
>
>
>David Booth, Ph.D.
>HP Software
>+1 617 629 8881 office  |  dbooth@hp.com
>http://www.hp.com/go/software
>
>Opinions expressed herein are those of the author and do not 
>represent the official views of HP unless explicitly stated 
>otherwise.


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Received on Monday, 3 March 2008 17:03:04 GMT

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