Re: Representing NULL in RDF

On 2013-06-09, at 20:36, Pat Hayes <> wrote:
>>> - value uknown (it should be there but the source doesn't know it)
>> Actually that piece of information could be written down in a RDF Schema graph like this:
> It can be written far more simply in RDF just by using a blank node:
> :a :p _:x .

Yes, a blank node is probably the closest thing to a SQL NULL in RDF.

Though it would be safer/clearer to write:

:a :p [] .

To emphasise the (NULL = NULL) → FALSE behaviour, which is key to the uses of NULL in SQL.

However, the convention in RDF is just to omit the property for that subject where something is unknown - as others have said.

- Steve

Steve Harris
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Received on Monday, 10 June 2013 10:48:33 UTC