RE: Representing NULL in RDF

Hi David,

I don't believe this is quite right, as RDF semantics make no assumptions about what the absence of a proposition/statement means. Only more constrained/expressive languages like OWL define this clearly, and in fact, in OWL it is quite the opposite.

The Open World Assumption used in OWL holds that the absence of a statement cannot be construed to mean the statement is false. The truth-value is independent of its presence/absence. (How "false" maps to "null" is another questions.)

Cheers
Michael

-----Original Message-----
From: David Wood [mailto:david@3roundstones.com] 
Sent: Montag, 3. Juni 2013 09:44
To: Jan Michelfeit
Cc: public-lod@w3.org
Subject: Re: Representing NULL in RDF

Hi Jan,

That's because nulls are generally not represented in Linked Data by design.  One "represents" a null by failing to include the relationship.  

Regards,
Dave


On Jun 3, 2013, at 4:38, Jan Michelfeit <michelfeit.jan@gmail.com> wrote:

> Hi,
> I was doing some comparison of relational databases and Linked Data and ran into the problem of representing an equivalent of database NULL in RDF.
> 
> I was surprised I haven't found any material or discussion on this topic (found only [1]) - is there some?. I believe it would be beneficial if this question was answered somewhere for future reference. I started a question on Stack Overflow [2] where I think it will be easier to discover and so that this list won't get polluted.
> 
> I'm aware of the open world assumption in RDF, but NULL or a missing value can have several interpretations, for example:
> 
> - 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)
> 
> I would like to known whether there is some *standard or generally accepted* way of distinguishing these cases. If you have an answer, please put it on [2], is possible.
> 
> Thanks in advance,
> Jan Michelfeit
> 
> [1] http://lists.w3.org/Archives/Public/public-rdf-wg/2011Nov/0167.html
> [2] http://stackoverflow.com/q/16873174/2032064
> 
>

Received on Monday, 3 June 2013 15:29:11 UTC