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Re: The notion of a "classification criterion" as a class

From: doug foxvog <doug@foxvog.org>
Date: Sun, 25 Apr 2010 01:08:38 -0400
Message-ID: <4BD3CE56.5080909@foxvog.org>
To: ontolog-forum@ontolog.cim3.net
CC: public-owl-dev@w3.org, robert.stevens@manchester.ac.uk, rector@cs.man.ac.uk

Benedicto Rodriguez <br205r@ecs.soton.ac.uk> wrote:

>  Thanks for the detailed reply as well!  It's very interesting that this thread caught your attention
>  because the original email was in part motivated by some findings regarding the application of the
>  Normalisation mechanism.  In fact, the main "building blocks" that I am using in the ontology models
>  from the :Person and :Wine domain examples are the Normalisation and "Specified Values" pattern that
>  you refer to.

>  However, even after using Normalisation and Specified Values (value partitions), I still "feel" the
>  need to somehow *explicitly* represent the classification criteria of "person by gender", "person
? by kinship", "wine by color" and "wine by grape" in the respective ontologies.  My first intuitive
>  attempt to do so, was to use OWL classes (:PersonByGender, ..., :WineByGrape) but I realized the
>  problems of this approach after Pat's and Doug's comments.

>  I'll try to summarize how I got to that point.  I'll use the :Wine domain example this time because
>  I think it helps better to see the generic case behind the modeling issue.  Using Normalisation and
>  Specified Values, a portion of the :Wine ontology model including 2 classification criteria (by
>  grape and by color) might look somewhat similar to this (please bear with me for the limitations of
>  illustrating the hierarchy structure using the text editor):

>  :Independent_Entity (aka :Self_Standing_Entity)

>     |-- :Grape
>         |-- :WineGrape
>             |-- :MerlotGrape
>             |-- :ChardonnayGrape
?            |-- (etc...)

>     |-- :Wine
>         |-- :MerlotWine
>         |-- :ChardonnayWine
>         |-- (etc... meaning rest of "wines by grape")

>         |-- :RedWine
>         |-- :RoseWine
>         |-- (etc... meaning rest of "wines by color"
>             although in this case, only :WhiteWine is left)

>         |-- :SpecificMerlotWineClass
>         |-- :SpecificRedWineClass
>         |-- :SpecificMerlotAndRedWineClass
>         |-- :SpecificChardonnayWineClass
>         |-- :SpecificWhiteWineClass
>         |-- :SpecificChardonnayAndWhiteWineClass
>         |-- (etc... meaning rest of "specific" wine classes that
>              we would need to represent and automatically classify
>              by the reasoner based on their "grape" and "color")

>  :Dependent_Entity (aka :Refining_Entity)
>     |-- :Value_Partition
>         |-- :WineColor
>             |-- :Red
>             |-- :Rose
>             |-- :White

I question this.  Is WineColor a subclass of Value_Partition, an
instance of Value_Partition, or something else?  Also, are :Red,
:Rose, and :White subclasses of :WineColor, instances of :WineColor,
or do they have some other relationship with :WineColorPartition?

Normally, a partition is an instance that identifies a base class
and a set of mutually disjoint subclasses which span the base class.
This is a binary relationship between a class and a set of classes.

OWL-DL disallows the first argument of a relation from being a class.
It also does not allow sets of classes to be defined.  So, defining
the partition as a relation in OWL-DL is not possible.  Defining the
partition as a class means that there are a number of instances of
the partition, which seems to violate the meaning of partition,
instantiation, or both.  The partition could be defined as an
instance, but relating the instance to a rule defining the meaning of
the partition is problematic.

>  Some notes/clarifications about this model:

>  * For space and simplicity, some important aspects of the Normalisation
>  mechanism have not been fully specified, such as the fact that the
>  subclasses of :Wine associated to a classification criterion are "defined
>  classes" (:MerlotWine, ..., WhiteWine) and the specific wine subclasses
>  to be automatically classified by the reasoner are "primitive classes"
>  (:SpecificXxxWineClass).  For example, [1] and [2] show the definitions
>  of :MerlotWine and :SpecificMerlotWineClass respectively.

This apparently is intended allow for a future definition of a WhiteMerlotWine.

>  These definitions would cause the reasoner to infer that
>  :SpecificMerlotWineClass is a subclass of :MerlotWine.  (Perhaps this link
>  might help illustrate what I'm trying to refer to:
>  http://www.gong.manchester.ac.uk/odp/html/Normalisation.html).

This reference does not duplicate classes with differently named subclasses
with the same apparent meaning.

>  * The "wine by color" classification criteria is represented using the
>  "Specified Values" value partition pattern.

>  And again, looking at the inheritance structure of the :Wine hierarchy now
>  *normalised*, it presents the *same* issue mentioned at the beginning of
>  my original email!

This is because the partitions were defined as subclasses of the classes
which they were intended to partition.  The partitions are objects which
can not be represented in OWL-DL.

>  Which was that we could argue that the inheritance structure is not
>  satisfactory because "different concepts are represented by classes at
>  the same level".  Sorry for repeating myself, but the structure seems to
>  be "asking" for some classes to separate these different concept groups.

The classes it is asking for are classes of classes ("meta-classes").  But
since such can not be defined in OWL-DL, you have a problem.

>  The already mentioned :WineByColor, :WineByGrape and now maybe even a
>  :SpecificWine or :NamedWine or for consistency :WineByName classes.

These are classes of classes, not subclasses of Wine; therefore,
the below structure does not work.

>  The hypothetical inheritance structure would be:

>     |-- :Wine
>         |-- :WineByGrape
>             |-- :MerlotWine
>             |-- :ChardonnayWine
>             |-- (etc...)
>  ...

>  And so, this is my dilemma. The ontology is normalised and still
>  seems to "need" this :WineByClassificationCriterion classes.

You are using a tool that is unable to express such meta-classes.

>  Based on the replies gathered so far, the consensus seems to be
>  that using a class is not the best approach to represent a
>  "classification criterion" in OWL DL.

Correct.

>  Allow me to recap.  The suggestion instead, is to use a restriction
>  on a property to define the classes that form the "classification
>  criterion".

Not quite.  Classes defined by a given *pattern* of rule are all
classes of one meta-type.  Classes defined by a different pattern
are of a different meta-type.  OWL-DL allows one to define
multiple rules of the same pattern, but it does not allow the
definition of the rule *patterns*.

>  For example, :MerlotWine is the restriction of the property
>  :madeFromGrape to :MerlotGrape (see [1]),

Not the restriction itself, but the class defined by the restriction.

>  :RedWine is the restriction of the property :hasColor to :Red,

Again, :RedWine is the class *defined* by the restriction.

>  and so on.  However, as part of the Normalisation mechanism, all
>  these properties and restrictions are already asserted in the
>  ontology model!

Sure.

>  This leaves me thinking that the "vision" of  separating the
>  post-normalisation flat hierarchy of subclasses of :Wine (or
>  :Person or in general any other normalised :DomainConcept) into
>  homogeneous subgroups is *not really necessary or possible* after
>  all, given the semantics of OWL DL.

It is not possible using the semantics of OWL-DL.

The classes from the different meta-classes are not necessarily
disjoint, so making a flat hierarchy instead of a directed
acyclic graph is not possible.

It is possible to define the meta-classes in more powerful languages,
howerver.

-- doug

>  Not sure if everyone would agree with that as the final conclusion
>  but if that was the case, it would feel somehow kind of hard to accept.

>  ...

>  Any comments or feedback are indeed very welcome.

>  Regards,
>  Bene Rodriguez-Castro


The following two definitions are identical.  I'm guessing that
you intended to make the second one a rdfs:subClassOf :RedWine ;
-- doug

>  ----
>  [1] Definition of :MerlotWine.

:MerlotWine rdf:type owl:Class ;
         rdfs:subClassOf :Wine ;
         owl:equivalentClass [ rdf:type owl:Restriction ;
                               owl:onProperty :madeFromGrape ;
                               owl:someValuesFrom :MerlotGrape ] .

[2] Defintion of :SpecificMerlotWineClass.

:SpecificMerlotWineClass rdf:type owl:Class ;
         rdfs:subClassOf :Wine ,
                         [ rdf:type owl:Restriction ;
                           owl:onProperty :madeFromGrape ;
                           owl:someValuesFrom :MerlotGrape ] .


>  -----Original Message-----
>  From: Alan Rector [mailto:rector@cs.man.ac.uk]
>  Sent: Thursday, April 22, 2010 9:36 AM
>  To: Benedicto Rodriguez
>  Cc: ontolog-forum@ontolog.cim3.net; OwlED-list; Robert Stevens
>  Subject: Re: The notion of a "classification criterion" as a class
>
>  Benedicto
>
>
>  For a generic reference on the mechanism we call "Normalisation" which
>  addresses this issue, see
>  A. Rector 2003. Modularisation of domain ontologies Implemented in
>  description logics and related formalisms including OWL. Knowledge
>  Capture 2003. 121-128.
>  http://www.cs.man.ac.uk/~rector/papers/Modularisation-normalisation-
>  rector.pdf
>
>  Robert Stevens, copied on this email, has an extensive family history
>  ontology that addresses all these issues.
>
>
>  In principle we would address issues of this sort following the
>  reference above  as something like:
>
>
>  Independent_entity
>     ...
>     Person
>
>
>  Dependent Entity
>     Value_partition
>        Gender
>           Male
>           Female
>
>
>  Plus properties such as
>  has_child
>  has_sibling
>
>
>  Then Parent == Person that has_child some Person.
>  Man == Person that has_gender some Male
>  etc.
>  (If you prefer you can see individuals for values such as male and
>  female; there are
>  tradeoffs in either approach.  See the W3C Best Practice note on
>  "Specified Values".
>  http://www.w3.org/TR/swbp-specified-values/ )
>
>
>  It would be nice to define the relation has_sibling in terms of
>  has_child, but this is tricky, since if you use the natural
>  representation:
>
>
>  inv(has_child) o has_child -->  has_sibling
>
>
>  then everybody is their own sibling. There's no easy way around this.
>
>
>  As to categories such as "Person by Gender" that might be defined in
>  OWL as
>  "Person that has_gender some Gender", there are two problems: one
>  technical and one philosophical.
>
>
>  The technical problem is that if you have made the generic assertion
>  that all people have genders,
>  Person subclassOf has_gender some Gender
>  Then
>  Person_by_gender is logically equivalent to Person.
>
>
>  If you are willing to forgo the generic statement, then you can create
>  the subclass.
>
>
>  The Philosophical problem concerns the status of classes such as
>  "Person by Gender" which many ontologists deplore as not being a proper
>  "universal".  From a purely logical point of view, this need not be a
>  problem.  In practice such constructs are commonly used in OWL KBs for
>  convenience, but best defined to reflect the developer's intentions, so
>  that as the KB evolves, the reasoner keeps the KB consistent with those
>  intentions.
>
>
>  Regards
>
>
>  Alan
>
>
>
>
>  On 15 Apr 2010, at 20:30, Benedicto Rodriguez wrote:
>
>
>        Hello everyone,
>
>        Apologies for cross-posting but I thought the email might be
>  relevant to both mailing lists: ontolog-forum@ontolog.cim3.net and
>  public-owl-dev@w3.org.
>
>        I am trying to put together an ontology design pattern (or
>  combination of patterns) with the intent of modeling multiple
>  alternative classification criteria of a domain concept.  At this
>  point, I have to commit my focus to OWL (or more specifically, to an
>  expressivity level within OWL-DL).
>
>        In the process I have come across what I think it is an
>  interesting modeling scenario. Let me use a simple example to describe
>  it extracted from [1].  Consider the following set of classes (as a
>  subset of a larger ontology model) in the popular domain of "family
>  relationships" organized according to the following subsumption
>  hierarchy:
>
>        :Person
>            |-- :Man
>            |-- :Woman
>            |-- :Parent
>            |-- :Child
>            |-- :Sibling
>
>        We could argue that this inheritance structure is not
>  satisfactory because different concepts are represented by classes at
>  the same level.  That is, the concept of gender, represented by the
>  classes :Man and :Woman, and the concept of kinship relationships,
>  represented by the classes :Parent, :Child and :Sibling.  In that
>  sense, the concepts of gender and kinship could be seen as two
>  different classification criteria for all the subclasses of :Person.
>
>        The issue that I am trying to solve deals with how to incorporate
>  the representation of these classification criteria concepts into the
>  ontology model.
>
>        An initial approach (kind of intuitive to me) would be two
>  represent the two classification criteria as classes (say
>  :PersonByGender and :PersonByKinship) and regroup all the subclasses of
>  :Person accordingly. The result would look like:
>
>        :Person
>            |-- :PersonByGender
>            |   |-- :Man
>            |   |-- :Woman
>            |-- :PersonByKinship
>                |-- :Parent
>                |-- :Child
>                |-- :Sibling
>
>        However, I see a conceptual problem with this model regarding the
>  subsumption relation between :Person and the classification criteria
>  classes :PersonByGender and :PersonByKinship, given that:
>
>        - Who would be the individuals of classes such as :PersonByGender
>  and :PersonByKinship? For example, if we consider :John and individual
>  of type :Man, we can say that :John is also of type :Person.  But does
>  it make sense to say that :John is of type :PersonByGender???
>
>        - Are these classes :PersonByGender and :PersonByKinship in fact
>  meta-classes? (If I could use an analogy with object-oriented design,
>  it is as if these two classes could be seen as abstract or deferred
>  classes).
>
>        This type of modeling scenario can be found in many concepts from
>  various domains (essentially any concept whose individuals/instances
>  could be grouped according to multiple different classification
>  criteria). Below is another popular example in the OWL literature
>  modified to fit into the same scenario and illustrate the problem [2]:
>
>        :Wine
>            |-- :WineByColor
>            |   |-- :WhiteWine
>            |   |-- :RedWine
>            |   |-- (etc.)
>            |-- :WineByGrape
>                 |-- :PinotGrigioWine
>                 |-- :MerlotWine
>                 |-- :CabernetSauvignonWine
>                 |-- (etc.)
>
>        In this case the classification criteria of :Wine are wines based
>  on their color and wines based on their type of grape.  Like in the
>  example of :Person, the classification criteria classes :WineByColor
>  and :WineByGrape seem intuitive choices to group the rest of all
>  subclasses of :Wine.  However, the subsumption relation between :Wine
>  <-  :WineByColor and :Wine<- :WineByGrape seems problematic.  Who
>  would be the individuals of classes such as :WineByColor or
>  :WineByGrape?
>
>        In general terms, the subsumption relation between a
>  :DomainConcept and a :ClassificationCriterion for that concept seems a
>  bit controversial.  For example, It does not seem to fit into one of
>  the 4 kinds of is-a relations defined by Johansson[3] plus  I think it
>  would violate the constraints of the OntoClean evaluation as well.
>  (Even though, for the most part I understand the theory behind the
>  OntoClean method and I think it is very useful, I personally find it a
>  bit difficult to apply coming from a software developer background).
>
>        In summary, after this lengthy introduction, below are the
>  questions that I am trying to answer:
>
>        - Are subsumption relations such as :Person<- :PersonByGender or
>  :Wine<- :WineByGrape acceptable?
>
>        - Can classes such as :PersonByGender or :WineByGrape be
>  "correctly" represented in the ontology model?  That is, classes that
>  correspond to a "classification criterion" and that may not have
>  individuals (or extensional representation) in the real world.
>
>
>        - Are there some guidelines or good-practices on how to represent
>  concepts that correspond to a"classification criterion" of the domain
>  concept that is being modeled?
>
>        Thanks a lot for any comments you may have!
>
>        (For the record, I'll mention that this work is part of my PhD
>  research.  One aspect of the overall idea is trying to adapt faceted
>  classification design guidelines to ontology design.  The notion of
>  "facet" and "classification criterion" seem to be fairly similar.
>  Identifying a reasonable representation of a "classification criterion"
>  in an ontology can help to bridge the gap between these two design
>  methodologies and that's the reason for the examples above.  Finally, I
>  would like to present if possible, the overall outcome as an ontology
>  design pattern or combination of them).
>
>        Regards,
>        Bene Rodriguez-Castro
>
>        Postgraduate Student | Intelligence, Agents and Multimedia Group
>  | School of Electronics and Computer Science | University of
>  Southampton | Southampton SO17 1BJ | United Kingdom | Phone: +44 23
>  8059 4059 | Email: b.rodriguez@ecs.soton.ac.uk
>
>        ----
>        [1]
>  http://protege.cim3.net/file/pub/ontologies/generations/generations.owl
>        [2] http://protege.cim3.net/file/pub/ontologies/wine/wine.owl
>        [3] Ingvar Johansson. Four kinds of is_a relations: genus-
>  subsumption, determinable-subsumption, specification, and
>  specialization. In WSPI 2006: Contributions to the Third International
>  Workshop on Philosophy and Informatics, Saarbrucken, 2006.
>
>
>
>  -----------------------
>  Alan Rector
>  Professor of Medical Informatics
>  School of Computer Science
>  University of Manchester
>  Manchester M13 9PL, UK
>  TEL +44 (0) 161 275 6149/6188
>  FAX +44 (0) 161 275 6204
>  www.cs.man.ac.uk/~rector
>  www.co-ode.org
>  http://clahrc-gm.nihr.ac.uk/
>
>
>
>
>
>
>
>
>
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Received on Monday, 26 April 2010 09:34:55 GMT

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