- From: Jeen Broekstra <jeen@aduna.biz>
- Date: Tue, 04 Nov 2003 15:56:33 +0100
- To: "Seaborne, Andy" <Andy_Seaborne@hplb.hpl.hp.com>
- Cc: www-rdf-rules@w3.org
Seaborne, Andy wrote: > I'm not quite clear on the query: > > Does this query give a sequence of "graphlets", one per soltuion > to the FROM clause, or a single graph of all the triples from all > the solutions? It returns a single result set, consisting of statements that match the from clause. It's not necessarily a single graph because the results from different matches may well be disconnected, but there is no explicit support for identifying these individual matches, if that's what you mean: you get one set of statements that contains all answers. > Another sort fo related question: in the case where the result of > a query is a subgrapgh of the original, does anyone know of any > literature describing algorithms for this subgraph calculation > that is faster than simply taking each solution and merging (that > can lead to a lot of unnecessary work)? Now I'm confused :) What do you mean with merging in this context? Filtering duplicate statements? If so, then I can't help you with literature refs from the top of my head, but we have implemented this by pushing a DISTINCT modifier down to the SQL engine to filter out duplicate variable-binding combinations, and an additional triple filter on top of that. We haven't spent too much time on optimizing this, but sofar it has not given us any serious performance problems. Of course this approach is only used when the user specifies a DISTINCT modifier in the SeRQL query, so it might just not have come up yet :) Cheers, Jeen -- jeen@aduna.biz Aduna (formerly Aidministrator b.v.) - http://www.aduna.biz Julianaplein 14b, 3817 CS Amersfoort, The Netherlands tel. +31-(0)33-4659987, fax. +31-(0)33-4659987
Received on Tuesday, 4 November 2003 09:55:27 UTC