- From: Christopher Welty <welty@us.ibm.com>
- Date: Mon, 11 Nov 2002 14:38:02 -0500
- To: www-webont-wg@w3.org
In the Guide, we tried to address the terminology somewhat in the passage
included below (from the Introduction). I suggest updating the final
paragraph below to include a statement like the one Jim wants, that gives
a name to RDF documents that use tags defined in an OWL ontology:
OWL is a language for defining Web ontologies and their associated
knowledge bases. Ontology is a term borrowed from philosophy that refers
to the science of describing the kinds of entities in the world and how
they are related. In OWL, an ontology is a set of definitions of classes
and properties, and constraints on the way those classes and properties
can be employed. An OWL ontology may include the following elements.
taxonomic relations between classes
datatype properties, descriptions of attributes of elements of classes,
object properties, descriptions of relations between elements of classes,
and, to a lesser degree,
instances of classes and
instances of properties.
Datatype properties and object properties are collectively the properties
of a class.
A set of OWL assertions loaded into a reasoning system is called a
knowledge base (KB). These assertions may include facts about individuals
that are members of classes, as well as various derived facts, facts not
literally present in the original textual representation of the ontology,
but entailed (logically implied) by the semantics of OWL. These assertions
may be based on a single ontology or multiple distributed ontologies that
have been combined using defined OWL mechanisms.
While ontologies for the most part do not include instances of classes (as
distinct from knowledge bases), it is often the case that some instances
are needed in an ontology to define certain classes. For example, if we
consider Wine and Color to be classes, and red to be an instance of Color,
then the class Red Wine would require the instance red as part of its
definition and thus as an element of the ontology.
Dr. Christopher A. Welty, Knowledge Structures Group
IBM Watson Research Center, 19 Skyline Dr.
Hawthorne, NY 10532 USA
Voice: +1 914.784.7055, IBM T/L: 863.7055
Fax: +1 914.784.6078, Email: welty@us.ibm.com
Deborah McGuinness <dlm@ksl.stanford.edu>
11/11/2002 12:37 PM
To: Christopher Welty/Watson/IBM@IBMUS
cc: www-webont-wg@w3.org
Subject: Re: SEM: Light review of semantics document
I have had a lot of discussions with people about what ontologies are in
common usage. I think the only thing that we all agree on is that there
is a
spectrum of descriptions for ontologies. I dont know that we want to get
into
a big description of it since i dont think the discussion is short. if
people
want to refer to something on the topic, i wrote about it in an
"ontologies
come of age" paper [1]. that paper includes a spectrum that a number of
us
came up with and i refined after a panel at aaai on ontologies.
Thus, i would be careful below with wording such as ontologies
referring "to what we "traditionally" ... call ontology in Computer
Science,
and "knowledge base" to refer to a mixture of ontology and instance data."
including class descriptions in our ontologies means including some
instances
because of hasValue and oneOf.
Since someone will ask the question - I wanted to head it off here. We
should
NOT say that owl documents with instances in them are not to be referred
to
as ontologies.
I agree with jim's point though that a document with only instances and
their
associated class tags in it is not what i think of as an ontology and
also is
not something that i would like to promote as a way of using the term.
i am not opposed to instance data set for this.
i do not usually make a big deal of a distinction between knowledge bases
and
ontologies since the overlap is too great and many people consider
knowledge
bases ontologies. I had not thought about this point directly in the
guide
writing but it probably would not create as much confusion if we downplay
that
distinction in the guide.
deborah
[1]
http://www.ksl.stanford.edu/people/dlm/papers/ontologies-come-of-age-abstract.html
Christopher Welty wrote:
> Jim,
>
> If by, "I believe strongly that this is not a critical issue of language
> design, it's simply a suggestion we develop consistent terms so we
> get our message out," you mean that you just want a term that we will
> agree to employ in our human interchange, and not something in the OWL
> language, then that's fine, make something up and we'll add it to the
> Guide.
>
> It appeared from the discussion that Jeff and you wanted something more
> formal, that required an adjustment to the meaning of the owl:ontology
> tag.
>
> In the Guide, Mike and I chose to employ "ontology" (not the tag, but
the
> natural language term) to refer to what we "traditionally" (it's a short
> tradition) call ontology in Computer Science, and "knowledge base"
> to refer to a mixture of ontology and instance data. We did not draw
> the distinction you want there, but if I understand you
> correctly, the Guide is right place to talk about this.
>
> -Chris
>
> Dr. Christopher A. Welty, Knowledge Structures Group
> IBM Watson Research Center, 19 Skyline Dr.
> Hawthorne, NY 10532 USA
> Voice: +1 914.784.7055, IBM T/L: 863.7055
> Fax: +1 914.784.6078, Email: welty@us.ibm.com
>
> Jim Hendler <hendler@cs.umd.edu>
> Sent by: www-webont-wg-request@w3.org
> 11/09/2002 06:59 PM
>
> To: Christopher Welty/Watson/IBM@IBMUS, www-webont-wg@w3.org
> cc:
> Subject: Re: SEM: Light review of semantics document
>
>
>
> At 3:00 PM -0500 11/8/02, Christopher Welty wrote:
> >I have to agree with Pat here, guys. The meaning of an "owl:ontology"
> tag
> >inside an RDF document is simply that the document contains OWL syntax,
> >not some hard to pin down notion of a separation between definitions
and
> >data.
> >
> >What you, Jeff and Jim, want to accomplish can be done with comments,
> >since the distinction you want does not exist in the language nor in
its
> >interpretation - it only exists in the minds of some people. I think
> what
> >you want is sort of like the distinction C compilers make for ".h"
files
> -
> >in point of fact there is no difference between the contents of a ".h"
> >and ".c" file, just a methodology enforced by some compilers.
> >
> >That using "ontology" to describe a set of instances does not match
your
> >definition is not, I think, the point. Maybe the tag is
inappropriately
> >named. But don't get me started on mis-named tags. "Property" is
> already
> >a LOT worse.
> >
> >-Chris
>
> Chris/Pat - I think you guys misunderstood me - I believe that all of
> these things are OWL documents, but I'm concerned with a small matter
> of usage. The way I see it, there are documents which are clearly
> owl ontologies because they define terms and properties and the like.
> There are also owl documents that only use those terms and, in fact,
> there is no reason that there will be any trace of any OWL vocabulary
> in those documents. For example, if Chris defines an ontology about
> people, I could have a document which contains only the following:
>
> Namespace definitions to RDF and to Chris' document
>
> <rdf:RDF>
> <chris:person rdf:id="Hendler" />
> </rdf:RDF>
>
> by the definition "uses owl terminology" this is NOT and owl
> document. By the definition "uses terms from an owl ontology" this
> is an Owl document.
>
> So I am asking for terminology that would
> i. let me differentiate this document from an arbitrary RDF
> document (and Pat, please note I wasn't being anti-logical, but it
> seems to me we don't need this distinction to have a logical meaning
> in the formal sense -- I'm simply looking for a common term to mean
> RDF documents that are expecting to be linked to owl ontologies) --
> Jeff called this a data document, which Pat didn't like.
> ii. lets me differentiate this kind of document from an owl
> document which does contain class and property definitions and
> restrictions. I DO KNOW what to call the ones that have that (an
> ontology), but not what to call the other ones.
>
> I believe strongly that this is not a critical issue of language
> design, it's simply a suggestion we develop consistent terms so we
> get our message out.
> Technically, it is clear to me the document above is an RDF document
> - it would use the RDF Model Theory and all would be happy. But
> colloquially, we need to be able to discuss these documents with a
> term that people in the outside world can understand.
>
> In class, I refer to these as "Owl data sets" and the students get
> it, I'd be happy with that term.
>
> So, I ask Pat/Chris and anyone else inclined to help out:
>
> what name shall we use for documents that are in the class with the
> following properties:
>
> Document a rdf:RDF document AND
> Document uses terms from a owl ontology document AND
> Document NOT a owl ontology document.
>
> IMHO, If we call such a document an "ontology," we're going to
> confuse a lot of people.
>
> Finally, such documents not only will, but DO exist (in case someone
> is going to argue that this is specious) -- there's a number of
> examples in [1], for example [2] which has no hint of the daml
> namespace in it, but is linked to an ontology which is clearly
> defined in DAML [3].
>
> [1] http://www.daml.org/data
> [2] http://www.daml.org/2002/02/chiefs/af.daml
> [3] http://www.daml.org/2002/02/chiefs/chiefs-ont
>
> >Dr. Christopher A. Welty, Knowledge Structures Group
> >IBM Watson Research Center, 19 Skyline Dr.
> >Hawthorne, NY 10532 USA
> >Voice: +1 914.784.7055, IBM T/L: 863.7055
> >Fax: +1 914.784.6078, Email: welty@us.ibm.com
> >
> >
> >
> >
> >pat hayes <phayes@ai.uwf.edu>
> >Sent by: www-webont-wg-request@w3.org
> >11/08/2002 11:34 AM
> >
> > To: Jim Hendler <hendler@cs.umd.edu>
> > cc: www-webont-wg@w3.org
> > Subject: Re: SEM: Light review of semantics document
> >
> >
> >
> >
> >>Sorry Pat, but I gotta agree with Jeff on this one- you signed onto
> >>this group which had "ontology" in the title, fully knowing by
> >>charter we would create something called an ontology language.
> >
> >Well, sure, but apparently what you and Jeff meant by 'ontology'
> >wasn't what I meant. Thats the trouble with English, right? Which is
> >one reason why we are doing all this in the first place...
> >
> >><owl:ontology>
> >> statements
> >></owl:ontology>
> >>
> >>was in DAML+OIL, has been in OWL from day 1, a prereq for WG members
> >>was familiarity w/D+O, so you should have been aware that was there.
> >
> >I have no problem with that, but I have always understood this to
> >simply be an XML marker for the presence of OWL syntax in the RDF
> >graph. Why do we need to say anything more than that? "owl:ontology"
> >isn't in the graph, right? So its not in the namespace, and it has no
> >semantics. If "owl:ontology" is in the OWL namespace, then we ought
> >to say what an RDF triple which includes that name means.
> >
> >>The issue we need to address is that IN ENGLISH USAGE (not formal
logic)
> >
> >I do wish you would make at least an effort to disguise your built-in
> >anti-logical knee-jerk, Jim. It just gets in the damn way. What we
> >are all doing here, whether you like it or not, is using ENGLISH to
> >talk ABOUT a FORMAL logical language. When using ENGLISH it is often
> >a good idea to use words which refer to concepts that actually make
> >some sense in the context being talked about.
> >
> >>there is a need for us to say whether there is a difference between
> >>documents that look like
> >>
> >><rdf:RDF>
> >>
> >><owl:ontology ... />
> >>...
> >>
> >><owl:class rdf:about="Moose">
> >> <owl:restriction>
> >> etc
> >> </owl:restriction>
> >></owl:class>
> >>
> >></rdf:RDF>
> >>
> >>and documents that look like
> >>
> >><rdf:RDF>
> >>
> >><a:Moose rdf:id="MyMoose />
> >>
> >></rdf:RDF>
> >>
> >>(and those which mix some of both).
> >
> >The difference is that one of them contains OWL syntax and the other
> >does not. End of story.
> >
> >What about the many other cases, such as <rdf:RDF>....</rdf:RDF>
> >which contains non-ground RDFS, say? What about one of those that
> >contains RDFS which would break fast-OWL? What do we call those? If
> >some RDF uses rdf:bag, is it instance data? What about an rdf:List,
> >described using bnodes? You (and Jeff) are confusing two different
> >distinctions: ground versus non-ground, and RDF vs OWL. That is a
> >dangerous confusion to incorporate into an official terminology.
> >
> >>Jeff's usage is consistent with the outside world's usage, and I
> >>suggest if we don't use it we will confuse everyone in the world
> >>except for logicians
> >
> >I'm tempted to respond that anyone who you would classify as a
> >non-logician is already confused in any case. But I won't.
> >
> >>-- given that, I'd suggest we use it -- i.e.
> >>
> >>Ontology documents are those that define classes and properties.
> >>Instance documents are defined by using RDF to produce instances (or
> >>individuals) that are members of those classes with those properties.
> >
> >Sorry, I object to this, because it doesn't make sense. You are
> >presuming something that is false: that RDF can only be used to
> >describe ground facts. We ought to use a naming convention that warns
> >the world not to get this confused, rather than casting the confusion
> >in stone.
> >
> >I know that RDF is often used for instance data, but it can be used
> >for other things. I frequently meet people in the DAML community who
> >are surprised to hear that RDF allows bnodes; there is deployed
> >software with serious bugs arising from the misunderstanding that RDF
> >is used only for ground facts. Also, this convention makes nonsense
> >of the fundamental presumption that one can merge RDF graphs. If
> >OWL/RDF really is RDF then this terminological usage becomes
> >nonsensical even when applied to actual documents. It already doesn't
> >make any semantic or operational sense.
> >
> >Pat
> >
> >>
> >>OWL documents include each or documents which combine both.
> > >
> >>I'm happy if someone wants a different term for "instance" documents.
> >>
> >>I think the above is consistent with our current documentation. I'm
> >>happy to see someone suggest rewording the above (Written quickly
> >>and not formally) in a way that is more technically correct -- but
> >>this is how most of the rest of the world will refer to what we
> >>have, so we should make it easy for them....
> >> -JH
> >>
> >>
> >>
> >>
> >>
> >>
> >> 1:42 PM -0600 11/7/02, pat hayes wrote:
> >>>>Pat, there is a terminology problem here. What you and Peter call
> >>>>ontologies are different from what I call ontologies.
> >>>
> >>>Yeh, I had that impression. My problem is that I don't really know
> >>>what you are talking about. I have never come across any useful
> >>>definition of "ontology" in our non-philosophical sense other than
> >>>something like "set of sentences" or maybe a document containing a
> >>>a set of sentences, etc.. If there is a real difference in your
> >>>mind between ontologies and other OWL thingies, then we ought to
> >>>get this clear and incorporate it into the language in some way.
> >>>
> >>>>My practical
> >>>>definition is that OWL ontologies are only those OWL documents that
> >>>>include the <owl:Ontology> tag.
> >>>
> >>>Hmm, I have to confess that I wasn't aware that 'owl:Ontology' was
> >>>in the OWL namespace. What is it supposed to mean?? Does it appear
> >>>in the RDF graph anywhere?
> >>>
> >>>But OK, an ontology is a *document*. In what language? I'm guessing
> >>>it has to be in OWL/RDF/XML, right? So an OWL/RDF graph is not an
> >>>ontology(?)
> >>>
> >>>>All other OWL documents are not OWL
> >>>>ontologies. Now, you are correct that a document with <owl:Ontology>
> >>>>could consist of nothing but ground facts, and as such you don't
> >>>>technically need to have a separate class of document for data.
> >However,
> >>>>the fact is, people only use the <Ontology> tag when they are
defining
> >>>>vocabularies (this statement is based on common usage in DAML). Are
> you
> >>>>suggesting that these people should include <Ontology> tags is all
of
> >>>>their documents (see daml.org's list of data sets for a number of
> >>>>examples of DAML documents without these tags)?
> >>>
> >>>I really don't give a rats about this tag, to tell you the truth,
> >>>but certainly people should somehow mark their OWL as being OWL; if
> >>>they don't, then they can't complain if an OWL engine misses it
> >>>entirely. We might want to follow RDF's lead and register an OWL
> >>>media type, though I think that idea is wrong-headed, myself. All I
> > >>care about is that we have some way to detect well-formed OWL which
> >>>is being asserted. Well-formed OWL means what it means as defined
> >>>by the OWL specs. The distinction between ground and non-ground OWL
> >>>is unimportant, seems to me, and there is no need to even refer to
> >>>it. If some piece of OWL has 10|6 ground facts and one non-ground
> >>>fact, I'm cool with that. What would you call it? Data with a dash
> >>>of ontology?
> >>>
> >>>>Or are you suggesting
> >>>>that we should call these ontologies too?
> >>>
> >>>If we use the term at all, then yes, they are ontologies, in much
> >>>the same sense that a gazetteer is a book.
> >>>
> >>>> I think the later would really
> >>>>confuse users to call every document an ontology, but only some
> >>>>ontologies are <Ontology> ontologies. In any case, all of our
> documents
> >>>>need to be a lot more clear about terminology (e.g., which
definition
> >of
> >>>>ontology does our WG use) and about how people should use ontologies
> to
> >>>>describe real content.
> >>>
> >>>As to the last point, the distinction between ontology and data
> >>>just seems to make things more confusing, suggesting a distinction
> >>>in meaning that isn't there.
> >>>
> >>>Pat
> >>>
> >>>>
> >>>>Jeff
> >>>>
> >>>>pat hayes wrote:
> >>>>>
> >>>>> >pat hayes wrote:
> >>>>> >>
> >>>>> >> >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?
> >>>>> >>
> >>>>> >
> >>>>> >Part of this depends on what you consider OWL. From your
> response,
> >I
> >>>>> >assume that you think of OWL as just a language for defining
> >ontologies,
> >>>>> >and that you must use it with RDF in order to describe data
> >>>>>
> >>>>> No. I fail to see the distinction you are drawing between
> 'ontology'
> >>>>> and 'data'. I don't know what you mean by this, or what
importance
> >it
> >>>>> has. One can have valid OWL documents which consist of nothing
but
> >>>>> ground RDF facts. So?
> >>>>>
> >>>>> >(e.g., a
> >>>>> >product catalog, a univeristy's course offerings, etc.). I tend
> to
> >think
> >>>> > >of OWL as an extension to RDF, so this data is still part of
> OWL,
> >it
> >>>>> >just has the standard RDF syntax.
> >>>>> >
> >>>>> >In any case, our model theory must talk about data to the same
> >extent
> >>>>> >that it talks about ontologies.
> >>>>>
> >>>>> It does. It always has done. What is the problem?
> >>>>>
> >>>>> Pat
> >>>>>
> >>>>> --
> >>>>>
> ---------------------------------------------------------------------
> >>>>> IHMC (850)434 8903 home
> >>>>> 40 South Alcaniz St. (850)202 4416 office
> >>>>> Pensacola (850)202 4440 fax
> >>>>> FL 32501 (850)291 0667
cell
> >>>>> phayes@ai.uwf.edu
> http://www.coginst.uwf.edu/~phayes
> >>>>> s.pam@ai.uwf.edu for spam
> >>>
> >>>
> >>>--
> >>>---------------------------------------------------------------------
> >>>IHMC (850)434 8903 home
> >>>40 South Alcaniz St. (850)202
> >4416 office
> >>>Pensacola (850)202
> >4440 fax
> >>>FL 32501 (850)291 0667 cell
> >>>phayes@ai.uwf.edu
> >http://www.coginst.uwf.edu/~phayes
> >>>s.pam@ai.uwf.edu for spam
> >>
> >>
> >>--
> >>Professor James Hendler hendler@cs.umd.edu
> >>Director, Semantic Web and Agent Technologies 301-405-2696
> >>Maryland Information and Network Dynamics Lab. 301-405-6707
> >(Fax)
> >>Univ of Maryland, College Park, MD 20742 240-731-3822
> >(Cell)
> >>http://www.cs.umd.edu/users/hendler
> >
> >
> >--
> >---------------------------------------------------------------------
> >IHMC (850)434 8903 home
> >40 South Alcaniz St. (850)202
> >4416 office
> >Pensacola (850)202
> >4440 fax
> >FL 32501 (850)291 0667 cell
> >phayes@ai.uwf.edu
> >http://www.coginst.uwf.edu/~phayes
> >s.pam@ai.uwf.edu for spam
>
> --
> Professor James Hendler hendler@cs.umd.edu
> Director, Semantic Web and Agent Technologies 301-405-2696
> Maryland Information and Network Dynamics Lab. 301-405-6707
> (Fax)
> Univ of Maryland, College Park, MD 20742 240-731-3822
> (Cell)
> http://www.cs.umd.edu/users/hendler
--
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
(voice) 650 723 9770 (stanford fax) 650 725 5850 (computer fax) 801
705
0941
Received on Monday, 11 November 2002 14:38:46 UTC