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Re: [ontolog-forum] Levels

To: Kathryn Blackmond Laskey <klaskey@xxxxxxx>
Cc: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Pat Hayes <phayes@xxxxxxx>
Date: Thu, 15 Feb 2007 13:02:37 -0600
Message-id: <p0623090dc1fa5c970a63@[]>
>  >If by 'subject matter' you mean that it is in the
>>universe of discourse, yes. But all sorts of
>>things are in the universe of discourse of any
>>reasonably complicated assertion: your TAMU
>>example may well refer to numbers, dates,
>>time-intervals, publications, etc.. If you use
>>'imports' it also refers to ontologies
>>(considered as Web entities). If this bothers
>>you, you shouldn't be using 'imports'. You can
>>always grab the actual ontology text using a Web
>>browser and cut and paste it into your document,
>>if you don't want to use an imports statement.
>Imports are fundamentally different from cut-and-paste.  That's
>because in an open world environment, things change.  The specs tend
>to ignore this issue, but it's very real.    (01)

That is true, and you are correct that it is an 
important distinction. I spoke too hastily above.    (02)

>If somebody changes the ontology I imported (I know they're not
>"supposed" to, but people on open networks do things they're not
>"supposed" to do), then my ontoloyg changes.    (03)

Actually that isn't necessarily the case. It 
depends, unfortunately, on how the imports is 
implemented. In the model theory we require that 
the name used to identify the ontology is a rigid 
identifier, thereby ruling out changes. As you 
say, this does not always comport with the way 
that things actually are, but then the way things 
actually are might not conform to the specs.    (04)

>  If the organization that
>created an ontology I import goes bankrupt and their server goes down
>and the ontology disappears and references ground out in a 404, then
>my ontology is broken.    (05)

A 404 error is not a sign of the ontology being 
broken, it is a sign that the network is broken. 
The Web often breaks in this way, and 
applications have to be able to handle it. The 
way that the CL model theory is written, an 
imports which accesses no ontology is trivially 
true, ie is semantically vacuous; but the spec 
allows this to be considered an error condition 
also. The OWL specs simply say nothing about this 
case.    (06)

>If I cut and paste, then the snapshot of the ontology that existed in
>the cut and paste is what I get, and how it stays.    (07)

True. Of course you may get a 404 error here as well.    (08)

>  However, the
>semantic information (yes, it's semantic information, not about the
>domain for which the ontology was constructed, but about my ontology)
>that I imported Ont-X is lost, except perhaps in some
>non-machine-interpretable comments I write in my ontology.  In other
>words, the link from my ontology to the ontology I imported is gone.    (09)

True, and I agree an important point. But if one 
were to take the attitude towards 'imports' that 
Chris was adopting, I think this fact would be 
considered unimportant.    (010)

Pat    (011)

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