Re: Representing NULL in RDF

On Jun 3, 2013, at 10:28 AM, Panzer,Michael wrote:

> 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.

Well, actually it does. Absence of a proposition means exactly that its truthvalue is undetermined, unless of course it is entailed by something that is present. This is true for RDF and all RDF semantic extensions, including OWL.

> 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

and in RDF

> 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.)

All true. Although I don't think it is ever correct to map "null" to "false".

Pat

> 
> 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
>> 
>> 
> 
> 
> 
> 
> 

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Received on Monday, 3 June 2013 17:07:57 UTC