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[protege-discussion] protege-discussion Digest, Vol 80, Issue 8

Csongor Nyulas csongor.nyulas at stanford.edu
Mon Apr 8 12:05:47 PDT 2013


Hi Andre Luiz,
Please see my answers below...

On 04/05/2013 05:00 PM, André Luiz Tietböhl Ramos wrote:
> Hello everyone,
>
> It took me some time to answer the replies to my previous post. Read 
> below please.
>
> On Thu, 2013-03-07 at 12:04 -0800, 
> protege-discussion-request at lists.stanford.edu wrote:
>
>> Today's Topics:
>>
>>     1. Re: Nothing class (newbie question) (Michael DeBellis)
>>     2. Re: protege-discussion Digest, Vol 80, Issue 7
>>        (Andr? Luiz Tietb?hl Ramos)
>>     3. Re: protege-discussion Digest, Vol 80, Issue 7 (Matthew Horridge)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>>
>> As a fellow newbie one thing I find very useful is the "?" icon on any information the
>> inferencer has inferred about your ontology. You can click on that and see why it thinks some of your classes are subclasses of Nothing.?
>> Michael DeBellis
>>
>> --- On Wed, 3/6/13, Csongor Nyulas <csongor.nyulas at stanford.edu  <mailto:csongor.nyulas at stanford.edu>> wrote:
>>
>> From: Csongor Nyulas <csongor.nyulas at stanford.edu  <mailto:csongor.nyulas at stanford.edu>>
>> Subject: Re: [protege-discussion] Nothing class (newbie question)
>> To:protege-discussion at lists.stanford.edu  <mailto:protege-discussion at lists.stanford.edu>
>> Date: Wednesday, March 6, 2013, 11:55 AM
>>
>> Also, if the reasoner classifies some classes as subclass of owl:Nothing
>> it means that those classes are unsatisfiable, or as Matthew said, they
>> cannot have any instances. This may be due to some modelling errors in
>> your ontology.
>>
>> Csongor
>
> Thanks Csongor.  As far as my limited knowledge goes in this subject, 
> I don't understand the satisfiable/unsatisfiable concept.  
> "Structure-wise" the classes' tree seems ok to me.  You
> meant that instances are be developed in the sense of having 
> individuals linked to them or by linking to other classes which are 
> then part of given individuals' links?  In fact, the
> instance concept is not very clear to me, sorry.  I don't see any a 
> "more defined" concept than data and object properties (which aren't 
> used for instances I suppose)
> and individuals.  BTW, do you consider individuals as instances?

I think the best would be if you would read an OWL Tutorial. [1] is 
quite comprehensive, [2] is less detailed but more visual and explains 
SWRL too, and [3] is useful if you want to understand the OWL language.

And yes, when I used instance I meant individual. In OWL the instances 
of a class are called individuals.

>
>> On 03/06/2013 11:24 AM, Matthew Horridge wrote:
>> > Hi,
>> >
>> > owl:Nothing is interpreted as the empty set.? It does not have any instances.? Because it is interpreted as the empty set, it is a subclass of every other class (since the empty set is a subset of every set).? owl:Thing appears at the top of the class hierarchy, whilst owl:Nothing appears at the bottom of the class hierarchy.? Hope this helps.
>> >
>> > Cheers,
>> >
>> > Matthew
>> >
>> >
>> >
>> > On 6 Mar 2013, at 11:12, Andr? Luiz Tietb?hl Ramos wrote:
>> >
>> >> Hello,
>> >>
>> >> What does the Nothing class mean actually?? Assuming its superclasses are inferred, I have many in it and do not know what this aspect means for sure.
>> >>
>> >> Thanks in advance.
>> >>
>> >> --
>> >> Andr? Luiz Tietb?hl Ramos
>> >>http://www.feng.pucrs.br/~andreltr  <http://www.feng.pucrs.br/%7Eandreltr>
>>
>> On Wed, 2013-03-06 at 12:04 -0800,
>> protege-discussion-request at lists.stanford.edu  <mailto:protege-discussion-request at lists.stanford.edu>  wrote:
>> > Message: 2
>> >
>> > Hi,
>> >
>> > owl:Nothing is interpreted as the empty set.  It does not have any instances.  Because it is
>> > interpreted as the empty set, it is a subclass of every other class (since the empty set is a
>> > subset of every set).  owl:Thing appears at the top of the class hierarchy, whilst owl:Nothing
>> > appears at the bottom of the class hierarchy.  Hope this helps.
>>
>>
>> Yes, it does.  I don't think this matters much though but the Nothing is
>> shown in the top of the tree and in red.  Since I'm just beginning  I'm
>> modeling as much as I can using classes and leaving individuals for a
>> step later.  In other words, how to define an instance although at this
>> point I don't need them AFAIK?

Even if you don't define any individuals in an ontology yourself, a 
reasoner can detect that some classes are defined in a way that it is 
impossible for those classes to have any instances (i.e. no individual 
can possible belong to that class).
For example, if you say that a class called "RedGreenCat" is defined as 
a "Cat that has color both Green and Red", but somewhere else in your 
ontology you state that a cat can have only one color, and "Green" and 
"Red" are not the same, then a reasoner would detect that your 
RedGreenCat class is unsatisfiable (i.e. it can have no instances 
whatsoever), and would classify it as a subclass of owl:Nothing.

>>
>> Message: 4
>> Date: Wed, 06 Mar 2013 11:55:56 -0800
>> From: Csongor Nyulas <csongor.nyulas at stanford.edu  <mailto:csongor.nyulas at stanford.edu>>
>> To:protege-discussion at lists.stanford.edu  <mailto:protege-discussion at lists.stanford.edu>
>> Subject: Re: [protege-discussion] Nothing class (newbie question)
>> Message-ID: <51379F4C.80909 at stanford.edu  <mailto:51379F4C.80909 at stanford.edu>>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> Also, if the reasoner classifies some classes as subclass of
>> owl:Nothing
>> it means that those classes are unsatisfiable, or as Matthew said, they
>> cannot have any instances. This may be due to some modelling errors in
>> your ontology.
>>
>> Csongor
>>
>>
>> Interesting opinion...  What kind of modeling errors could there be?
>> Should I understand my modeling is somewhat flawed then?  As it is it
>> seems ok to me even though I'm from more computer programming/modeling
>> focus, UML specifically.

There could be many types of modelling errors. As somebody suggested, 
you can click on the question mark icon (which are useful especially in 
the inferred views), to learn why a reasoner thinks a given statement is 
true.
I would suggest, again, to read the tutorial(s) to have a better 
understanding of how to correctly model ontologies in OWL.

>
> -- 
> Andre Luiz Tietbohl Ramos
> http://www.feng.pucrs.br/~andreltr <http://www.feng.pucrs.br/%7Eandreltr>
>
>
>
>
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Regards,
Csongor

[1] http://owl.cs.manchester.ac.uk/tutorials/protegeowltutorial/
[2] http://dior.ics.muni.cz/~makub/owl/
[3] http://www.w3.org/TR/owl2-primer/
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