- From: Seaborne, Andy <andy.seaborne@hp.com>
- Date: Fri, 02 Sep 2005 14:25:32 +0100
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Enrico Franconi wrote: > Hi all. > We would like to submit some comments on the "SPARQL Query Language > for RDF" document, to be found in [1]. > > Our main goal is to be able to work on a future document about the > semantics of (various parts of) SPARQL. > We would like to identify fragments of SPARQL from a "core" language > to a "full" language, and to work on formalising the semantics of the > core language first and then extend it to cover the more complex > languages. > With the exception of the last comment in [1], our comments are not > revealing any major impediment for the definition of a well founded > model theoretic semantics for SPARQL. > As a first exercise, in [2] we already worked out the formal > semantics for core SPARQL and we also give some complexity result. > We have a major concern on the possibility of giving any clear > semantics to the querying provenance part, which we probably would > prefer to leave out of the normative document. > > cheers > --e. > > [1] <http://www.inf.unibz.it/krdb/w3c/sparql-notes-fub.pdf> > [2] <http://www.inf.unibz.it/krdb/w3c/rdf-sparql-semantics.pdf> > > Enrico Franconi - franconi@inf.unibz.it > Free University of Bozen-Bolzano - http://www.inf.unibz.it/~franconi/ > Faculty of Computer Science - Phone: (+39) 0471-016-120 > I-39100 Bozen-Bolzano BZ, Italy - Fax: (+39) 0471-016-129 > > Enrico, Re: UNION and OPTIONAL equivalence. Taking an example from rq23: ==== Data @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . _:a rdf:type foaf:Person . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@example.com> . _:b rdf:type foaf:Person . _:b foaf:name "Bob" . ==== Query1: PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name . OPTIONAL { ?x foaf:mbox ?mbox } } ==== Results1: ---------------------------------------- | name | mbox | ======================================== | "Alice" | <mailto:alice@example.com> | | "Bob" | | ---------------------------------------- using your transformation: ==== Query2: PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { { ?x foaf:name ?name } UNION { ?x foaf:name ?name . ?x foaf:mbox ?mbox } } ==== Results2: ---------------------------------------- | name | mbox | ======================================== | "Alice" | | | "Bob" | | | "Alice" | <mailto:alice@example.com> | ---------------------------------------- [[There was a discussion on the DAWG comments with Bob MacGreggor and Geoff Chappell about different ways of formulating OPTIONAL that woudl give additional context here.]] Andy
Received on Friday, 2 September 2005 13:26:09 UTC