- From: Richard Cyganiak <richard@cyganiak.de>
- Date: Wed, 2 Mar 2011 23:54:58 +0000
- To: Pat Hayes <phayes@ihmc.us>
- Cc: RDF-WG WG <public-rdf-wg@w3.org>
Hi Pat, Wow, this is unexpected! On 2 Mar 2011, at 22:47, Pat Hayes wrote: > So here's an idea. See if this flies. [snip] > This keeps all the advantages of blank nodes for human use (chiefly, that their IDs can be short and can be re-used as often as one likes, and don't need to be globally unique) while keeping the underlying RDF free from all the blank-node issues that keep giving people headaches. In my eyes, the problem isn't blank nodes per se. In RDF Concepts, blank nodes are ~5 paragraphs. They are easy enough to understand. A graph can have anonymous nodes that don't have a global identifier. No big deal. The problem is that RDF Semantics then defines these nodes as things that can be multiplied and merged in ways that is just way over most people's head. And all that complexity just doesn't seem to do anything useful in practice! Ignoring the question of charter scope for a minute: I'd like to know how RDF Semantics would have to be changed to define blank nodes as “normal” graph nodes that “just” don't happen to have a global/persistent identifier. I believe this is also what Marcelo and colleagues proposed in [1] for the RDF Next Steps workshop. Or alternatively, since everyone (including the SPARQL and OWL WGs) seems to like RDF Concepts, but ignores or hates parts of RDF Semantics: Can we refactor the specs so that the good parts would be separated from the unnecessarily complicated stuff? Best, Richard [1] http://www.w3.org/2009/12/rdf-ws/papers/ws23 > > We can also require that all RDF processors be able to input existing RDF notations which have syntactic forms for blank node identifiers, either by storing the RDF in this form or by skolemizing it on input. This sets up a backward-compatible situation which is strongly biassed to eliminate blank nodes as rapidly as possible from actual deployed RDF. We can even call these tag-labelled nodes "blank nodes" if we like, with only a tiny change to the current RDF concepts specifications. > > OK, I will send this now and wait for the hurricane to start. > > Pat > > [1] http://www.ietf.org/rfc/rfc4151.txt > [2] http://lists.w3.org/Archives/Public/semantic-web/2011Mar/0053.html > > On Mar 2, 2011, at 1:35 PM, Richard Cyganiak wrote [on semantic-web@w3.org]: > >> Reto, >> >> On 2 Mar 2011, at 18:50, Reto Bachmann-Gmür wrote: >>>> Is there any practical difference between bnodes and normal nodes, >>>> except the scope (and necessity) of their name? >>> >>> Yes, a graph with bnodes can potentially be simplified: the same meaning may be expressed with a more lean graph, i.e. with less nodes and triples. If all your nodes are uris you cannot do simplifications with rdf entaillment. >> >> Reality check please! >> >> When was the last time you saw such a non-lean RDF graph in the wild, outside of examples and test cases? Can you name a production system that routinely performs the simplification you talk about, with user benefit? >> >> The question was about practice. You describe a thought experiment. I think it's a good example of a complication in RDF that was added for sound theoretical reasons, but has failed to deliver any value whatsoever in practice. >> >> Best, >> Richard >> >> > > ------------------------------------------------------------ > IHMC (850)434 8903 or (650)494 3973 > 40 South Alcaniz St. (850)202 4416 office > Pensacola (850)202 4440 fax > FL 32502 (850)291 0667 mobile > phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes > > > > > >
Received on Wednesday, 2 March 2011 23:56:51 UTC