Re: Representing NULL in RDF

Just for the record, I was suggesting the blank node only to represent the ***case described below***, not as a general replacement for NULL, which seems to have many meanings. In the original message this was one of four or five possible NULL meanings. 

Pat

On Jun 12, 2013, at 11:08 AM, Tim Berners-Lee wrote:

> 
> On 2013-06 -10, at 19:48, Steve Harris wrote:
> 
>> On 2013-06-09, at 20:36, Pat Hayes <phayes@ihmc.us> 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.
> 
> 
> Surely a null in  an RDF database conveys no information about the 
> thing, unless you have out of band knowledge. 
> If you have NULL for a cellphonenumber, then that normally means no one stored a cellphone number,
> but it doesn't mean that there is a cellphone whose number is unknown.
> 
> A blank node means "There exists one."   As in "This person has some cellphone number".
> which is very different.
> 
> Nulls should be converted.
> 
> Tim
> 

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Received on Friday, 14 June 2013 00:21:56 UTC