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Re: SEM: Light review of semantics document

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 6 Nov 2002 23:08:47 -0600
Message-Id: <p05111b04b9efa4c4093c@[65.217.30.130]>
To: Jeff Heflin <heflin@cse.lehigh.edu>
Cc: www-webont-wg@w3.org

>Here's some initial comments on the Semantics document dated Nov. 3:
>
>1) Sect. 2.2. The syntax needs the ability to represent documents that
>consist soley of facts (that is, something other than ontologies).

? Can you explain what you mean by "other than ontologies" ?Do you 
mean, not in OWL?

>Perhaps a top-level <content> or <data> production could be added. The
>most import reason for this is that content documents (which are not
>ontologies), will also need to be represented. Assuming imports is not
>postponed, such documents will also need to contain imports directives.
>
>2) In the abstract syntax we have EquivalentClasses,
>EquivalentProperties but SameIndividual. We should change them all to
>the same basic form. Since sameXXXas is what is used in the exchange
>syntax, I suggest: SameClass, SameProperty, and SameIndividual.
>
>3) Section 3.4: The discussion of imports does not take into account
>documents that are not ontologies. I had a proposal (that I thought you
>agreed to), that fixed this and other problems. Is this an oversight, or
>are you waiting for the group to resolve the issue before making a
>change.
>
>4) Sect. 4.1: The conditino for n-triple form seem overly restrictive.
>Is this just meant for OWL/DL?
>
>5) Same section: The list of URI references that should not be mentioned
>should include owl:imports (assuming it is not postponed)
>
>6) Sect. 5.2: I'm hesitant about all of the iff definitions. For
>example, isn't iff for TransitiveProperty putting an undue burden on
>reasoners? I understand that you can only infer something is an
>owl:TransitiveProperty if it is transitive in all models, but it seems
>that you might be able uses cardinalities to restrict a property to a
>certain number of tuples and then list all of these tuples. In such a
>case, wouldn't complete reasoners always have to run through at the
>tuples to determine if the property was transitive? Seems like an
>expensive operation to me and I don't really see the utility of it.
>
>Also, as I was reading the following thing occured to me, which is not
>specific to the semantics document:
>
>The notion of complementOf in an open-world like the Semantic Web
>worries me.

RIGHT!! I have been complaining about this ever since it was first 
put into DAML. We should have a relative complement construction as 
basic, rather than an absolute one, since we never know when one 
ontology's universe is the same as another's.

>We can never compute the complement because we can never
>know the entire set of resources. I guess this will be used in rules in
>such a way that we never actually need to know the extension of the
>complement of a class, but are we sure there are no problems lurking
>here? Is this something that should be a new issue, or have people given
>this enough thought and decided its okay?

No, they havn't, and its not OK, and it needs some thought.

Pat


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Received on Thursday, 7 November 2002 00:08:30 GMT

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