- From: Steve Harris <steve.harris@garlik.com>
- Date: Thu, 12 Mar 2009 16:23:00 +0000
- To: SPARQL Working Group <public-rdf-dawg@w3.org>
On 12 Mar 2009, at 13:43, Seaborne, Andy wrote: > > >> -----Original Message----- >> From: public-rdf-dawg-request@w3.org [mailto:public-rdf-dawg- >> request@w3.org] On Behalf Of Steve Harris >> Sent: 12 March 2009 10:33 >> To: SPARQL Working Group >> Subject: Re: [sub-select] Some examples and discussion >> >> On 12 Mar 2009, at 06:39, Lee Feigenbaum wrote: >>> The idea of using ASK queries in expressions appeals to me as well, >>> though it doesn't necessarily read as well as !EXISTS in SQL. The >>> verbosity is similar though, I guess. >> >> Similar, and it's one less bit of syntax. My personal preference is >> for fewer, more flexible verbs. But it's just a matter of taste. >> >>> I'm curious as to the interplay between: >>> >>> projected expressions >>> sub-selects >>> assignment >>> >>> Is there a combination of these that makes the 3rd irrelevant? Or >>> pairs of them that are far more useful when included together? >>> That's the sort of thing I'm working to wrap my head around. >> >> Yes, if you have projected expressions then you effectively get >> assignments: >> >> SELECT ?x >> WHERE { >> ?x :age ?age . >> FILTER(?age >= ?min_age) >> (SELECT 18 AS ?min_age) >> } >> >> Is equivalent to: >> >> SELECT ?x >> WHERE { >> ?x :age ?age . >> FILTER(?age >= ?min_age) >> LET(?min_age := 18) >> } > > Steve - good example because it's different and a bit more tricky. > Let (err - no pun intended) me work though the details. This is a > more tricky example than the one I gave because syntactically you > assign after the use of ?min_age in the FILTER which raises the > necessary question of scope and order. Yeah, I did that deliberately to provoke the question of scope. At the time of writing I was in favour of that working, but having doodled a bit I think it doesn't make much sense, and the scoping can be lexical order without any problems. - Steve -- Steve Harris Garlik Limited 2 Sheen Road Richmond TW9 1AE T +44(0)20 8973 2465 F +44(0)20 8973 2301 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 Thursday, 12 March 2009 16:23:40 UTC