- From: Steve Harris <steve.harris@garlik.com>
- Date: Fri, 5 Mar 2010 10:56:52 +0000
- To: Ivan Herman <ivan@w3.org>
- Cc: Andy Seaborne <andy.seaborne@talis.com>, sparql Working Group <public-rdf-dawg@w3.org>
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? - Steve -- Steve Harris, Garlik Limited 2 Sheen Road, Richmond, TW9 1AE, UK +44 20 8973 2465 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, 5 March 2010 10:57:20 UTC