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Re: DAML+OIL documentation ambiguous?

From: Matt Halstead <matt.halstead@auckland.ac.nz>
Date: Fri, 23 May 2003 16:15:01 +1200
Message-ID: <3ECDA045.8000100@auckland.ac.nz>
To: Yarden Katz <katz@underlevel.net>
CC: www-rdf-logic@w3c.org

"This _could_ suggest..." was my point

Just pointing out that someone could interpret that as meaning that 
specifying a property restriction demands that each instance of person 
has this property, especially when it's not easy to find a reference to 
the fact that property restrictions like this are optional.  I would bet 
object oriented people coming to DAML+OIL and trying to get to grips 
with DL based thinking could get the wrong interpretation.

Yarden Katz wrote:

>Matt Halstead <matt.halstead@auckland.ac.nz> writes:
>
>  
>
>>from http://www.daml.org/2001/03/daml+oil-walkthru#restrictions
>>
>>-----snip------
>>
>>The next few lines describe a class-specific range restriction. In
>>particular, the parent of a Person is also a Person.
>>
>>  <rdfs:subClassOf>
>>    <daml:Restriction>
>>      <daml:onProperty rdf:resource="#hasParent"/>
>>      <daml:toClass rdf:resource="#Person"/>
>>    </daml:Restriction>
>>  </rdfs:subClassOf>
>>
>>What happens here is that the Restriction defines an anonymous class,
>>namely the class of all things that satisfy the restriction. In this
>>case: the class of all things whose parent is a Person. We then demand
>>that the class Person is a subClassOf this (anonymous) class. In other
>>words: we demand that every Person must satisfy this Restriction,
>>which in this case amounts to demanding that Persons have only Persons
>>as their parents.
>>
>>-----snip------
>>
>>This could suggest the default cardinality is 1 in DAML+OIL, perhaps
>>it could be made clearer by saying that if a person does have this
>>property then it demands....
>>
>>Hmm, perhaps it is a minimum of 1, come to think of it, I can't find
>>where such a notion is explicitly stated.
>>    
>>
>
>Maybe I completely misunderstood your question, but why does the above
>imply any value for cardinality?  The snippet states, as you say, that
>in a triple (s hasParent o) where s is of type Person, then o must be
>of type Person as well.  However, this does not imply that an object
>of type Person must have a parent, therefore the cardinality is no way
>restricted to 1 or at least 1. 
>  
>
Received on Friday, 23 May 2003 00:15:06 GMT

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