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Re: CHAIR-NOTE: Defaults and etc.

From: Jim Hendler <hendler@cs.umd.edu>
Date: Fri, 25 Jan 2002 00:04:52 -0500
Message-Id: <p05101013b87692bea42b@[]>
To: Dan Connolly <connolly@w3.org>
Cc: webont <www-webont-wg@w3.org>
>On Thu, 2002-01-24 at 21:06, Jim Hendler wrote:
>>  *** To summarize - our mission is to reach consensus on the MINIMUM
>>  langauge we feel comfortable "forcing" everyone to use.
>on that much I agree, but your example makes me nervous...
>>  for example:
>>  :mammal a owl:class;
>>      :birthmethod
>>         [def:DefaultValue :LiveBear].
>>  :platypus a :mammal;
>>     :birthmethod :EggLaying.
>>  :cow a :mammal;
>>    That is what I do at the LANGUAGE level.
>>  Now what does that mean?
>>  This means any user who reads this is entitled to conclude all and
>>  only those facts above and entailed by them.  This (according to D+O
>>  semantics) means
>>  it would be legitimate to conclude
>>    :platypus :birthmethod :EggLaying.
>er... that much is stated in the input, yes, but...
>  >   :platypus :birthmethod [def:DefaultValue :LiveBear].

You are right - I left out the statement that platypus was a subclass 
of mammal, and that cow was a subclass of mammal - I should have made 
this explicit:

:platypus a owl:class;
   rdfs:subclass :mammal;
   :birthmethod :Egglaying.

:cow a owl:class;
   refs:subclass :mammal.

>now where do you get this?
>>    :cow :birthmethod [def:DefaultValue :LiveBear].
>and this? where does it come from?

and then, having made them explicit, it follows from
the DAML+OIL axiomatic semantics which stated

(<=> (PropertyValue subClassOf ?csub ?csuper)
      (and (Type ?csub rdfs:Class)
           (Type ?csuper rdfs:Class)
           (forall (?x) (=> (Type ?x ?csub)
                            (Type ?x ?csuper))))) [subClassOf axiom 2]

>>  and if you want to claim to be an OWL reasoner, you should be able to
>>  conclude those things.
>>  However, I being a smart fellow who wants to make more money than the
>>  people who don't have defaults, add some code to MY OWL processor
>your OWL processor? er... maybe your processor, but if it
>makes more conclusions than the OWL spec licenses, it's
>not an OWL processor any more. i.e. its conclusions can't
>be backed by the OWL spec.

sorry - my "Extended OWL-based Processor(TM)" which I have actually 
embedded into some web-management applications, so you as a user 
don't even know it exists.

>You can offer any sort of heuristic service you want that
>returns any sort of interesting (or otherwise) conclusions
>you want... but if you call it a W3C-OWL processor, I'll probably
>send the W3C-trademark/QA cronies after you.

agreed, but I just renamed it to avoid this problem :->

>>  1) I am free to add to the langyage and did so with defaults.
>no, your extension isn't consistent with the rest of the
>language, the way I see it.

what do you mean consistent with?  I use exactly the same triple 
store you do and return the same things you do when you check my 
triples against your semantics.  However, I added a new function 
called QUERY which was not standardized and can return whatever the 
heck I want.  If our language includes something called "Query" then 
I will call mine "def:DefaultBasedQuery" -- I have extended the 
coverage of the statements you made and added value, I have not in 
anyway compromised the semantics of the specified language -- that 
was my whole point.  Further, in practice I have probably embedded 
this in some application, so you as a user of my stuff only get my 
web site management package - so from your point of view as an 
outsider, all you see is a number of documents containing OWL 
statements using some predicates from def: (a document I have 
published on the web at URI http://.../DefaultPackage.owl )

>  > 2) DefaultValue was NOT a requirement of the language
>>  3) Those who don't like default reasoning are happy,
>Not when folks use your service for a while, then come
>to my service, which follows the spec, and they
>don't get their default conclusions any more.

yes, so they come back to mine because they like my extensions, and 
they stop using yours -- the market therefore decides that this kind 
of default is good.  If, however, people decide this is causing them 
problems, they'll stop using mine and use yours.  You (Dan) are the 
one who taught me that the market has to be what decides these 
things, I'm applying your principle!


>W3C process doesn't work that way. The chair can't decide
>the design.

addressed in previous message [1]

  - JH

[1] http://lists.w3.org/Archives/Public/www-webont-wg/2002Jan/0165.html

Prof James Hendler				hendler@cs.umd.edu
Dept of Computer Science			http://www.cs.umd.edu/~hendler
AV Williams Bldg				301-405-2696 (work)
Univ of Maryland				301-405-6707 (Fax)
College Park, MD 20853 USA
Received on Friday, 25 January 2002 00:05:03 UTC

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