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[protege-owl] How to assign NULL (un-assigne an instance) in SWRL rule?

Martin O'Connor martin.oconnor at stanford.edu
Thu Apr 12 15:01:53 PDT 2007


> Thanks for the tips. You mentioned that "Also, there is no null in 
> OWL: an individual either has a particular property with a value or it 
> does not". Does this mean that I have to chnage the property value to 
> another value in order to show unassigining. How about introducing a 
> NULL instance for each class and use it as NULL assignment?

You cannot change the value of a property with SWRL. If you assign a 
value to a property that already has a value, a second value will be 
added - the initial will not be retracted. If the property is 
functional, a classifier will indicate an error in this case. I have no 
idea what a NULL instance of a class is, but it will not help you get 
around the inability to retract existing values.

In OWL or SWRL, a retraction (if it were supported) would be a statement 
that an ontology is invalid. OWL and SWRL statements are logical 
assertions that should remain true forever (for a particular model).

> SWRL has not but I couldn't use (show) it in SWRL Editor, since the 
> Editor doesn't have such operator.


SWRL does not have negated atoms.

>
> As I understand it is not possible to show the dynamic behavior of an 
> Individual.
> For example Joining and Leaving to a Queue?

If a queue is an OWL concept, no. SWRL may not be an appropriate 
formalism here.

Martin

>
> regards,
> Shahab
> */Martin O'Connor <martin.oconnor at stanford.edu>/* wrote:
>
>
>     SWRL (or OWL) do not support retraction at the language level. An
>     OWL+SWRL ontology is a logical model and if SWRL statements in that
>     model cause assertions to be made that contradict previous assertions
>     then the model in inconsistent.
>
>     Also, there is no null in OWL: an individual either has a particular
>     property with a value or it does not - there is no empty value.
>
>     Martin
>
>     shahab wrote:
>
>     >Hi everyone,
>     >
>     >I am trying to write a SWRL rule in which the result of
>     implication would
>     >be un-assigning, breaking the already assigned relation , between two
>     >instances.
>     >for example :
>     >
>     >hasCurrentState(Queue_Inst, Queue_Contains) →
>     >hasCurrentState(Queue_Inst, NULL??? ),
>     >
>     >in which domian (hasCurrentState) = Queue and Queue_Inst is an
>     individual
>     >of Queue,
>     >and range (hasCurrentState) = QueueState and Queue_Contains is an
>     >individual of QueueSatate,
>     >
>     >Now the problem is that how can I show the NULL instance( no
>     instance)?
>     >How can I break this relation between two instances in SWRL rules
>     in SWRL
>     >Tab?
>     >
>     >regards,
>     >
>     >
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