- From: Ivan Herman <ivan@w3.org>
- Date: Fri, 05 Mar 2010 15:04:18 +0100
- To: Steve Harris <steve.harris@garlik.com>
- CC: Andy Seaborne <andy.seaborne@talis.com>, sparql Working Group <public-rdf-dawg@w3.org>
- Message-ID: <4B910F62.3080109@w3.org>
On 2010-3-5 11:56 , Steve Harris wrote: > On 5 Mar 2010, at 08:02, Ivan Herman wrote: >> >> On 2010-3-4 15:53 , Andy Seaborne wrote: >>> In >>> http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2010Feb/0018.html >>> >>> >>> >>> Rob Vesse observes that "no duplicates" is at odds with the expansion of >>> a simple path (a term we have already decided to remove) into a triple >>> pattern because there is an implicit projection going on. >>> >>> {?x foaf:knows{2} ?y} >>> is not quite the same as >>> { ?x foaf:knows ?z . ?z foaf:knows ?y } >>> when there are acylic components/ >>> e.g.: >>> >>> :a foaf:knows :b . >>> :a foaf:knows :c . >>> :b foaf:knows :d . >>> :c foaf:knows :d . >>> >>> because ?z is projected away. >>> >>> We can specify either way: >>> >>> + emphasis that certain property paths are the same as the triple >>> expansion form, and not have the striuct no duplicates rule (this >>> reintroduces the simple property paths concept) or >>> >>> + note, and provide an example, that they are not exactly equivalent. >>> >>> I prefer the latter - keep the "no duplicates" situation. >>> >> >> So do I. As a user, who does not know about the algebra and such, having >> ?x/:a and ?y/:d to the {?x foaf:knows{2} ?y} seems like the natural >> answer... > > Actually, naively I'd expect {?x foaf:knows{2} ?y} to do the same as {?x > foaf:knows ?tmp . ?tmp foaf:knows ?y}. On the other hand, I suppose > people might not care about cardinality in the property path case? Not > strong feelings I guess. > > What does this do to list handling though? If you have > :x :p (1 2 2 3) . > and > { :x rdf:rest*/rdf:first ?y } [or whatever the right combo is] > won't you get > ?y = 1, 2, 3 > as a result? > Ouch. You got me there:-( Ivan > - Steve > -- Ivan Herman, W3C Semantic Web Activity Lead Home: http://www.w3.org/People/Ivan/ mobile: +31-641044153 PGP Key: http://www.ivan-herman.net/pgpkey.html FOAF : http://www.ivan-herman.net/foaf.rdf vCard : http://www.ivan-herman.net/HermanIvan.vcf
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Received on Friday, 5 March 2010 14:04:08 UTC