Modelling an equivalent of database NULL in RDF

Question

I would like to know if there is a standard or generally accepted way of representing an equivalent of NULL used in databases for RDF data.

More specifically, I\'m inter

Answer 1

I do a bit of modelling in RDF. I know of no widely used vocabulary for representing the kind of information you are looking for. There is however a widely accepted pattern which is applicable.

In work I did about a year ago I had a similar requirement to represent properties with "nullable values". A property with a nullable value either had a value or a reason why the value wasn't present.

I represented this by introducing a b-node as the value of the property. That b-node would have either an rdf:value property linking to a value, or a reason property linking to a reason the value is not available, e.g.

:foo
   :aProp [a :nullableValue; rdf:value "value"] ;
   :bProp [a :nullableValue; :reason :notAvailable ]
.