- From: Steve Harris <steve.harris@garlik.com>
- Date: Wed, 14 Mar 2012 11:06:19 +0000
- To: "Polleres, Axel" <axel.polleres@siemens.com>
- Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, "public-rdf-dawg@w3.org" <public-rdf-dawg@w3.org>
On 2012-03-14, at 10:45, Polleres, Axel wrote: > (sorry, hot "send" to early) > >> Could you expand on "we need DISTINCT"? Is that just a technical >> point that DISTINCT covers more or a political point about the >> comments? > > For me this is definitly a technical point, since a DISTINCT-paths > -semantics, which can be optimized/efficiently implemented, doesn't > seem to be feasible by recognizing DISTINCT subqueries alone, > at least not trivially... > > I.e., while DISTINCT() can possibly be defined in terms of a rewriting > (which introduces fresh variables for blank nodes), I think that's neither > elegant nor very practical for optimizations without the explicit keyword, > whereas a syntactic element DISTINCT() gives a direct handle for > optimizations, right? > > So, I think this is important *both* technically and in in order > to address the comments. > >> What about the lesser case of just {*}{+} and *+ changes? > > I am fine with having those, but for the reasons above, I would > feel uncomfortable going without DISTINCT(). To speak bluntly, this seems crazy! Adding both DISTINCT and {*} {+} / * + is taking an already complex feature and making it a significant challenge to implement. - Steve -- Steve Harris, CTO Garlik, a part of Experian 1-3 Halford Road, Richmond, TW10 6AW, UK +44 20 8439 8203 http://www.garlik.com/ Registered in England and Wales 0535 7233 VAT # 849 0517 11 Registered office: Landmark House, Experian Way, Nottingham, Notts, NG80 1ZZ
Received on Wednesday, 14 March 2012 11:07:06 UTC