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[protege-discussion] Doubt about information structure

Csongor Nyulas csongor.nyulas at
Wed Apr 10 10:59:53 PDT 2013

Please read below...

On 04/10/2013 05:57 AM, André Luiz Tietböhl Ramos wrote:
>> >> On Wed, 2013-03-06 at 12:04 -0800,
>> >>protege-discussion-request at  <mailto:protege-discussion-request at>   <mailto:protege-discussion-request at>  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).
> Suppose I do not define some individuals related to a given class, or 
> classes, in an ontology consequently I'm assuming they'll be inferred 
> as subclasses of the Nothing, correct?

I assume that you are asking whether a class that does not have any 
individuals asserted in your ontology will be inferred as a subclass of 
owl:Nothing. This is NOT TRUE. A reasoner classifies a class as a 
subclass of owl:Nothing ONLY IF the given class CAN NOT have ANY 
individuals as it members. If a class COULD have a member (even if none 
is asserted in your ontology) the reasoner would not classify it under 

> Is it a mandatory condition to avoid classes being inferred as 
> subclasses of the Nothing class that there are relationships between 
> them and a individuals?

As I explained above: no.

> Theoretically, is it possible to have a class that is purely 
> conceptual thus is it is not linked to any individual?

Yes, that is correct.

> Would this condition mean it is an error in boolean sense?

This would not be a modelling error, and would not lead to unsatisfiable 
classes or an inconsistent ontology. There are many other modelling 
errors, though, which would lead you to unsatisfiable classes or 
inconsistent ontologies. The explanation support (through the question 
mark icons) are a good way to start "debugging" your ontology.


> Thanks,
> -- 
> André Luiz Tietböhl Ramos
> <>
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