Re: DAML-ONT: the case for closedness

I think there are a few notions of "closed" that people are using:

(1) Closed as in a definition may not change.  (this is not dependent upon whether
the class might have been a primitive class or defined class.)
One could insure this by essentially grabbing a version of the ontology at a
moment in time and then doing all of your work with respect to that version of the
ontology.
This is too restrictive though since then everyone would work with respect to
their own checkpointed versions of ontologies.

(2) Closed as in only trusted agents may modify a term.  A trusted source may only
be the author of the ontology or it may be a set of trusted agents (like a group
on unix).     A kid in the Philippines is unlikely to be designated as an
authoritative agent but potentially my ontology on wines may be designated as an
authoritative source/ontology and you may be willing to trust me that I will
update terms appropriately.  You may be willing to consistently use my wines
ontology even without checking to see if definitions have been modified since you
trust me.
You may also trust me to only allow people to change the ontology who are trusted.

If you think my ontology is valuable and you trust me to put a policy in place
that only allows updates that are valid, then you can use my ontology as it
evolves.  Then you do not have to be an expert in every domain.

(3) Closed as in a sufficient conditions for membership (defined classes in
description logics).  The class then has a complete definition.  We may however
find new instances of the class as new instances become known to the system.

(4) Closed in terms of no new elements of a class. Even if a new instance becomes
known to the system, it is guaranteed that it will not be an instance of the
closed class. One can effectively close a class in this sense in some frame
languages by putting a cardinality on the class that is equal to the current
number of known instances of a class. (for example, ontolingua allows this.)  In
languages with a one-of construct, these classes are inherently closed (unless of
course we allow someone to modify the elements in the one-of definition) since
there is an implicit maximum cardinality on the class.

(5) Closure of the fillers on a slot.  CLASSIC had a close operation that allowed
one to apply the closed world assumption to slots and say that the known fillers
of a slot are all of the known fillers.  that effectively added a maximum
cardinality restriction on the slot and thus did not allow new fillers to be
added.

I think the discussion was focusing on notion 2 above - who should be trusted to
modify a definition.  This in my opinion will be very important for collaborative
use of evolving ontologies.

I just wanted to point out that closure has a number of senses with respect to
ontologies.

Deborah McGuinness
dlm@ksl.stanford.edu

>
> From: Jeff Heflin (heflin@cs.umd.edu)
> Date: Thu, Oct 19 2000
>
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>   ------------------------------------------------------------------------
>
> Message-ID: <39EF4BEC.748BE87E@cs.umd.edu>
> Date: Thu, 19 Oct 2000 15:30:52 -0400
> From: Jeff Heflin <heflin@cs.umd.edu>
> To: "Hart, Lewis" <lhart@grci.com>
> CC: www-rdf-logic@w3.org
> Subject: Re: DAML-ONT: the case for closedness
>
> "Hart, Lewis" wrote:
> >
> >
> > To me the definition of 'globally agreed to' means a specified version
> > of the ontology, as given by its URL, which everyone who cares knows
> > about. The kid in the Philippines could publish whatever he wants, but
> > it doesn't mean anyone will use it. If an author intends to use the
> > agreed to meanings, then they must reference the appropriate defining
> > ontology:
> >
> > <rdf:RDF
> >   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
> >   xmlns:daml="http://www.w3.org/2000/08/daml-ont#"
> >
> >   xmlns:EC="http://www.e.commerce.org/standards/ontology#"
> >
> >   >
> >   <EC:Purchase_Order>
> >     ... blah blah blah
> >   </EC:Purchase_Order>
> > </rdf:RDF>
> >
> > If a different ontology (say xmlns:EC="http://hackers.net/ontology") is
> > referenced,
> > then you do not necessarily know what is meant. You may or may not trust it.
> >
>
> The problem comes not so much in interacting with a site or exchanging
> messages between agents (in which case certificates and/or case-by-case
> acceptance might work sufficiently), the problem comes with an
> "ontology-based" search engine. Here's an overly-simplified example:
>
> Let's say we have the following in our E-commerce ontology:
>
> Product isa Thing
> Computer isa Product
> ...
>
> Let's say someone has built the first quantum computer and is offering
> it for sale. They need to extend the E-commerce ontology with a special
> QuantumComputerOntology, which might include the following:
>
> QuantumComputer isa Computer
>
> Finally, on a web page this person now says:
>
> Q2000 instance-of QuantumComputer
>
> Let's say I'm in the market for a new computer. I might be interested in
> the QuantumComputer if I knew about it, but if I didn't know about the
> QuantumComputerOntology beforehand, I couldn't say that I trust this
> ontology. Thus, my query about Computers will never return this instance
> b/c I don't believe that "QuantumComputer isa Computer." In this case,
> it would be nice if my reasoner automatically used the new ontology, so
> that my query would return the Q2000 as well as more traditional
> computers.
>
> However, let's say that some hacker creates an ontology the extends the
> E-commerce ontology with this beauty:
>
> Thing isa Computer
>
> Now if my reasoner automatically accepts this ontology, I'm in for a
> world of trouble. It will tell me that everything is a computer!
>
> The problem is we want different behaviors depending on our a priori
> knowledge of the ontology. How do we make sure the right thing is done?
> I don't want users of the brave new web to be asked every minute by
> their computers if they accept John Doe's new ontology (which may be
> very complicated and contain implications that they don't understand),
> but I also don't want some guy selling widgets out his basement to have
> to wait 3 months for some certification body to say his ontology is
> trustworthy before people can even find out that he sells that kind of
> widgets! That goes totally against the distributed nature of the Web!
>
> Jeff
>
>   ------------------------------------------------------------------------
>
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--
 Deborah L. McGuinness
 Knowledge Systems Laboratory
 Gates Computer Science Building, 2A Room 241
 Stanford University, Stanford, CA 94305-9020
 email: dlm@ksl.stanford.edu
 URL: http://ksl.stanford.edu/people/dlm/index.html
 (voice) 650 723 9770    (stanford fax) 650 725 5850   (computer fax)  801 705
0941

Received on Thursday, 19 October 2000 21:20:51 UTC