- From: Enrico Franconi <franconi@inf.unibz.it>
- Date: Mon, 17 Jul 2006 23:07:29 +0200
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
On 17 Jul 2006, at 22:59, Enrico Franconi wrote: > My above answer makes sense only if all the variables in the query > are distinguished (SELECT *). However, in your example only ?X is a > disinguished variable (SELECT ?X), and therefore YES, the correct > answer should be, and is, {?X/Paul}, since the non-distinguished > variables ?Y and ?Z are interpreted existentially. > However, note that in order to write the above query you already > should have in mind the answer you expect. In other words, while > writing a query you can not expect the user to think in advance how > the answer could be and write the query accordingly. It can be > easily seen that if you want to reproduce with non-distingushed > variables the behaviour of bnodes in the answer set (like in the > above example), then the query with non-distinguished variables may > be exponentially larger than the answer set with bnodes. If you > think about it, this is due to the all possible different > coreferences between bnodes in the answer that you have to > explicitly represent in the query (this has also to do with the > cycles in the answer set I was mentioning a couple of emails ago). Also note that in SPARQL the variables in a basic graph pattern are all distinguished; the role of non-distinguished variables is played by the bnodes. --e.
Received on Monday, 17 July 2006 21:07:47 UTC