- From: Lee Feigenbaum <feigenbl@us.ibm.com>
- Date: Tue, 27 Mar 2007 15:37:23 -0400
- To: public-rdf-dawg-comments@w3.org, rnewman@franz.com
Richard Newman wrote on 02/25/2007 02:27:53 AM: > > DAWG, > > I have an implementation question for which I cannot find an > answer in the spec. > > Given a SELECT query for which some results are duplicated, and > which does not specify DISTINCT, is it acceptable for an > implementation to return DISTINCT (or partially DISTINCT) results? > > This is exercised by <http://www.w3.org/2001/sw/DataAccess/tests/ > #modifer-limit>: > > - with no DISTINCT processing, the results are [ 1, 1 ]. > - with DISTINCT processing, the results are [ 1, 2 ]. Thanks for bringing this to our attention. Please note that most of the tests in .../DataAccess/tests are not currently approved by the Working Group, and some of the tests explicitly do not reflect the specification. We are working to produce an updated and approved test suite at http://www.w3.org/2001/sw/DataAccess/tests/data-r2/ . This is still very much a work in progress, but will receive more attention with our recent publication of a Last Call working draft. > I seem to recall from informal sources that this is acceptable, > but it would be good to get a firm documented answer, particularly > when I can see that this could be contentious. The algebra within Section 12 of the Last Call draft defines the precise cardinality given by combining SPARQL graph patterns and the cardinality for matching basic graph patterns. These cardinalities are preserved when the ToList() operation is applied to generate a solution sequence. The DISTINCT operator appears in the algebra and specifies the exact effect of the DISTINCT keyword on solution cardinalities within the solution sequence. Note that the REDUCED keyword is an at-risk feature in the current Last Call draft that can modify the cardinalities of solutions within the solution sequence. It is defined in http://www.w3.org/TR/rdf-sparql-query/#modReduced . In the absence of the DISTINCT or REDUCED keywords, the specification gives a precise cardinality for the solutions that appear in the solution sequence. thanks, Lee > > Thanks, > > -R > >
Received on Tuesday, 27 March 2007 19:38:09 UTC