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

shahab pishava at
Thu Apr 12 00:17:21 PDT 2007

Dear Martin,

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?

Another question : Is it possible to have  logical "not" in SWRL rule. For example, I want ro say  : 
not(hasCurrentState(Queue_Inst, Queue_Contains))→ 
hasCurrentState(Queue_Inst,  NULL??? ),

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

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

Martin O'Connor <martin.oconnor at> 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.


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
>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
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