- From: Seaborne, Andy <andy.seaborne@hp.com>
- Date: Fri, 10 Dec 2004 17:51:18 +0000
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>

Pat, In email, you were asking about CONSTRUCT: Pat wrote: >>There is one case that Im a bit puzzled about, which is the >>CONSTRUCT answer where all the various answers are merged into a >>single answer (Is that right? It took me a while to figure out that >>is what was meant here, and I might not have it right.) So for >>example suppose the target graph is >> >>bill loves _:who . >>joe loves _:who . >> >>and the query is >> >>construct * where ?x loves ?y >> >>Now, as I understand it (and the definitions I sent say) , the >>result will be the graph merge of two sub-answers, which will >>themselves in this case be >> >> bill loves _:who . (first answer binding ?x/bill, ?y/_:who) >> >>and >> >>joe loves _:who . (second answer binding ?x/joe, ?y/_:who) >> >>But the merge of these will require the bnodes in the two >>sub-answers to be separated, so that one will get something like >> >>bill loves _:a >>joe loves _:b >> >>as the result graph in this case, which loses some information that >>was in the target. Is that what was intended? If not, the >>definitions need to be tweaked. The intent of the CONSTRUCT is that it should not create two different bNodes: ---- Data: @prefix : <http://example.org/ns#> . <bill> :loves _:who . <joe> :loves _:who . ---- cwm rule: @prefix : <http://example.org/ns#> . { ?x :loves ?y } => { ?x :knows ?y } . ---- and with cwm I get: <bill> :knows _:who . <joe> :knows _:who . that is, same bNode. Which, in SPARQL, is: PREFIX : <http://example.org/ns#> CONSTRUCT ( ?x :knows ?y ) WHERE ( ?x :loves ?y ) I see that "merge" is not the right language. Would this be better? """ The answer to a CONSTRUCT query: CONSTRUCT pat1 WHERE pat2 where pat1 is a basic pattern is the set of RDF triples X formed by the union of S(pat1) for all substitutions S where S is a solution of pat2. """ (a "solution" = "answer substitution" in your definitions) Now "CONSTRUCT * WHERE pattern" is supposed to be a shorthand for using the pattern as the template: "CONSTRUCT pattern WHERE pattern" Andy

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