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:da...@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....@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 > >
