- From: Seaborne, Andy <andy.seaborne@hp.com>
- Date: Thu, 25 Jan 2007 09:57:44 +0000
- To: Eric Prud'hommeaux <eric@w3.org>
- CC: public-rdf-dawg@w3.org
Eric Prud'hommeaux wrote: > * Seaborne, Andy <andy.seaborne@hp.com> [2007-01-24 20:15+0000] >> >> Eric Prud'hommeaux wrote: ... >>> 7 Matching Alternatives >>> >>> Query results involving a pattern containing GP1 and GP2 will >>> include separate solutions for each match where GP1 and GP2 give >>> rise to *different* sets of bindings. >>> >>> We talked about this some, too. Can't remember where we got. I prefer >>> to not have an implicit DISTINCT on UNION (something the SQL folks >>> regret). >> >> See the algebra: >> http://www.w3.org/2001/sw/DataAccess/rq23/rq25-algebra.html#defn_algUnion >> >> The cardinality in union is the sum of left and right cardinalities. > > ok, i hacked at the UNION text: > > Query results of GP1 <code>UNION</code> GP2 are all of the > solutions from GP1 and the solutions from GP2, in any order. > > Still not ideal as it leaves the possibility that the results are > either > > GP1a > GP1b > GP1c > GP2a > GP2b > GP2c > or > GP2a > GP2b > GP2c > GP1a > GP1b > GP1c > > vs > GP2b > GP2c > GP1a > GP1c > GP2a > GP1b > > but perhaps good enough as there is nothing saying that there is any > order to the constituent results. We really ought not to say anything about order - I can think of two reasonable implementation schemes that will give different orders (an index-scan based one and a recursive evaluation one). Andy
Received on Thursday, 25 January 2007 09:57:52 UTC