Re: Representing NULL in RDF

Hi Michael,

I agree in regard to OWL, of course.  I took Jan's question to relate to a generic Linked Data context since this is public-lod not (e.g.) public-owl-dev.

Regards,
Dave


On Jun 3, 2013, at 11:28, "Panzer,Michael" <panzerm@oclc.org> 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. 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 16:04:31 UTC