- From: Sven R. Kunze <sven.kunze@informatik.tu-chemnitz.de>
- Date: Mon, 10 Jun 2013 20:56:59 +0200
- To: Steve Harris <steve.harris@garlik.com>
- Cc: Pat Hayes <phayes@ihmc.us>, Jan Michelfeit <michelfeit.jan@gmail.com>, public-lod@w3.org
Zitat von Steve Harris <steve.harris@garlik.com>: > 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. > > Though it would be safer/clearer to write: > > :a :p [] . We are not talking about serializations. ;) > To emphasise the (NULL = NULL) → FALSE behaviour, which is key to > the uses of NULL in SQL. Excellent point! > However, the convention in RDF is just to omit the property for that > subject where something is unknown - as others have said. Jan asked about how to distinguish between his four cases which are indeed slightly different to each other. Omitting a triple has therefore a different quality than telling the existence of the property of this very subject. So, there is more information (existence) than when omitting the whole triple. -- Sven R. Kunze Chemnitz University of Technology Department of Computer Science Distributed and Self-organizing Systems Group Straße der Nationen 62 D-09107 Chemnitz Germany E-Mail: sven.kunze@informatik.tu-chemnitz.de WWW: http://vsr.informatik.tu-chemnitz.de/people/kunze Phone: +49 371 531 33882
Received on Monday, 10 June 2013 18:57:24 UTC