- From: Eric Prud'hommeaux <eric@w3.org>
- Date: Sat, 19 Jun 2004 05:17:05 -0400
- To: "Seaborne, Andy" <andy.seaborne@hp.com>
- Cc: public-rdf-dawg@w3.org
- Message-ID: <20040619091702.GB1385@w3.org>
On Fri, Jun 18, 2004 at 10:26:09PM +0100, Seaborne, Andy wrote: > > > > -------- Original Message -------- > > From: public-rdf-dawg-request@w3.org <> > > Date: > > > > On Fri, Jun 18, 2004 at 02:52:10PM +0100, Seaborne, Andy wrote: > > > > > > -------- Original Message -------- > > > > From: Kendall Clark <> > > > > Date: 18 June 2004 13:01 > > > > > > > > Folks, > > > > > > > > I'm not wedded to this wording, but I think it at least hints at an > > > > important requirement. Ideally I'd like some kind of first class > > > > syntax for a boolean query -- SELECT BOOL or SELECT ? or ASK -- but > > > > the requirement isn't as much about syntax as it is about being able > > > > to query a graph and get back TRUE or FALSE. > > > > > > An observation: if we have LIMIT and if we have the trailing flag, > > > "there was more", then "LIMIT 0" is the same as asking "does this > > > graph pattern match at all?" and it can be optimized as such on the > > > server - it would depend on the same decisions elsewhere for > > > disjunction. > > > > Or LIMIT 1 and no trailing flag. > > I think you can do all the same things with that. > > In the setting of querying an OWL inferred graph, it is possible to know of > the existence of a triple without knowing what it is: > > <c> rdfs:subClassOf > [ rdf:type owl:Restriction ; > owl:onProperty <p> ; > owl:minCardinality "1"^^xsd:nonNegativeInteger > ] . > > <x> rdf:type <c> . > > then > > (<x> <p> ?v) > > is true but the system may not know a specific value for ?v I see your point and call. I was arguing for just using a LIMIT of n+1 in order to promote simplicity and consistency. I think the complexity issues you raised would more than offset the simplicty of striking a flag in the protocol. So, in this scenario, a query with the boolean flag set expects an empty response with the boolean-ness set in the there-are-more-solutions flag. That seems managable (and definable). > Maybe system could return a bNode to indicate the existence of something > not determined and then the "LIMIT 1" approach works. Using bNodes like > this does get into an issue of when to stop as there are infinitely many > solutions to any query of at least one result which don't add any > information. That makes the interaction with LIMIT a bit tricky. > > Andy > > > > > > That is not to say that syntax for it would not be appropriate. > > > > admittedly -- -eric office: +81.466.49.1170 W3C, Keio Research Institute at SFC, Shonan Fujisawa Campus, Keio University, 5322 Endo, Fujisawa, Kanagawa 252-8520 JAPAN +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA cell: +1.857.222.5741 (does not work in Asia) (eric@w3.org) Feel free to forward this message to any list for any purpose other than email address distribution.
Received on Saturday, 19 June 2004 05:17:05 UTC