- From: Steve Harris <steve.harris@garlik.com>
- Date: Fri, 25 Mar 2011 16:01:10 +0000
- To: Pat Hayes <phayes@ihmc.us>
- Cc: Sandro Hawke <sandro@w3.org>, Michael Schneider <schneid@fzi.de>, Graham Klyne <GK-lists@ninebynine.org>, Dieter Fensel <dieter.fensel@sti2.at>, Enrico Franconi <franconi@inf.unibz.it>, Hugh Glaser <hg@ecs.soton.ac.uk>, Mark Wallace <mwallace@modusoperandi.com>, Alan Ruttenberg <alanruttenberg@gmail.com>, Reto Bachmann-Gmuer <reto.bachmann@trialox.org>, Ivan Shmakov <oneingray@gmail.com>, Ivan Shmakov <ivan@main.uusia.org>, "<semantic-web@w3.org>" <semantic-web@w3.org>
On 2011-03-25, at 15:41, Pat Hayes wrote: > > On Mar 25, 2011, at 10:05 AM, Sandro Hawke wrote: > >> Thanks for the detailed answer, but I'm pretty sure you're answering a >> different question than I meant. (Sorry for not being more clear.) >> What I meant was: is OWL 2 Full okay with people Skolemizing ontologies >> they are asserting? >> >> I might be misunderstanding, but it seems like all the problems you >> point out only arise during the entailment check. And yes, I know you >> can't Skolemize a query. I would never even think about doing that. >> I'm just talking about Skolemizing assertions. >> >> I think its general best to do queries in a query language and/or a rule >> language, but maybe that's a matter of taste. >> >> You say, "you never know how someone will use your graph", so I guess >> the point is that Alice might publish an ontology that gets Skolemized >> by her system, and then Bob publishes an identical ontology, and then >> when Charlie comes along and wants to find out whether Bob and Alice's >> ontologies entail each other, he's going to get a false negative because >> of the Skolemization. > > We can probably even fix this, in fact. If we can reliably distinguish 'bnode URIs' from other URis, eg if they all use a common namespace, then there is an obvious notion of graph equivalence which allows a 1:1 replacement of the skolem URIs. And then Charlie can discover that, though not logically equivalent, Alice and Bob's graphs are graph-equivalent. People will write code to check things like this if it ever starts to matter to anyone. The cost of testing this is identical to the cost of checking graph equivalence right now (its the same algorithm.) Exactly. In triplestores I'm familiar (admittedly not that many) with bNodes are skolemised into a value space that's different from both literals and URIs, so this is a natural consequence. - Steve -- Steve Harris, CTO, Garlik Limited 1-3 Halford Road, Richmond, TW10 6AW, UK +44 20 8439 8203 http://www.garlik.com/ Registered in England and Wales 535 7233 VAT # 849 0517 11 Registered office: Thames House, Portsmouth Road, Esher, Surrey, KT10 9AD
Received on Friday, 25 March 2011 16:01:46 UTC