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[protege-owl] how can I model NULL data values in OWL?

Timothy Redmond tredmond at stanford.edu
Wed Feb 22 09:36:19 PST 2012


On 02/22/2012 05:53 AM, Dennis Pierson wrote:
>
> Hi,
>
> I have instances with unpopulated values. Specifically I want to model 
> NULL dates. I can't find any mention of null or unpopulated datatypes 
> in the OWL or XSD documentation. Is there any way to do this? Pellet 
> won't accept it ("");
>

The real question here is what do you mean by this "NULL" value.  OWL 
lets you pick the semantics that you want (there are at least three 
possibilities).  I give an example of these these three cases in the 
attached ontology.

First, you could be creating an individual that you know cannot have a 
dateTime.  I have created an instance like this with the following axioms:

    Individual: knownNotToHaveADate
         Types:
             not (dateProperty some rdfs:Literal),
             Dated


This asserts that the individual knownNotToHaveADate cannot have any 
dateProperty property value.

Second, you could be asserting that a particular individual has a 
property value but you just don't know what it is.  I have created an 
instance like this with the following axioms:

    Individual: hasUnknownDate

         Types:
             dateProperty some xsd:dateTime,
             Dated


Here the individual hasUnknownDate has some dateProperty and this value 
is a dateTime but it is not known what value this property has.

Finally, you could have an individual where you don't know if or what 
dateProperty value it has.  In this case you don't have to say anything 
- OWL does not assume anything one way or the other.

I also made some test classes so that you can run a reasoner and see 
that the individuals classify into the right classes.  In particular the 
couldHaveADate individual is not found to be in either the MustHavaDate 
or the DatedButNoDate classes.

-Timothy

> Thank you
>
> Dennis
>
>
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