Re: Representing NULL in RDF

On 2013-06 -03, at 22:39, Jan Michelfeit wrote:

> Hi,
> thank you all for your answers.

> 
>> ... One "represents" a null by failing to include the relationship
>> ... RDF semantics make no assumptions about what the absence of a proposition/statement means
> 
> I agree. The question was actually about *distinguishing* between the mentioned cases.

Well, then you are not mapping from RDB to RDF.
As in the database the null didn't tell you which of your case
it is, of your options

> - value not applicable (the attribute does not exist or make sense in the context)
> - value uknown (it should be there but the source doesn't know it)
> - value doesn't exist (e.g. year of death for a person alive)
> - value is witheld (access not allowed)

You can have out of band, outside the table, information to tell you.
You can rely on assumptions you can make in given applications.

Both of which you can do with graphs too in exactly and precisely 
the same way.  You can have implicit or explicit assumptions
about what the absence of a statement means.

So basically IMHO a null maps exactly to no triple.

Tim