- From: Axel Polleres <axel.polleres@deri.org>
- Date: Fri, 18 Feb 2011 21:47:19 +0000
- To: SPARQL Working Group <public-rdf-dawg@w3.org>
- Cc: Lee Feigenbaum <lee@thefigtrees.net>, Paul Gearon <gearon@ieee.org>, Alexandre Passant <Alexandre.Passant@deri.org>, Andy Seaborne <andy.seaborne@epimorphics.com>
p.s.: I assume that the behaviour for Bnodes in INSERTs is rather the one we know from CONSTRUCT, i.e. having a new bnode per pattern solution. I realize that the - admittedly sketchy, but hopefully understandable - definition of Dataset() within [3] is wrong at the moment... "where Dataset(modify_template, P) is the RDF dataset obtained from taking each query solution in the solution sequence of P, substituting for the variables in the modify_template, and combining the triples into a single (named) RDF graph by set union." should be "where Dataset(modify_template, P) is the RDF dataset obtained from taking each query solution in the solution sequence of P, substituting for the variables in the modify_template, and combining the resulting graphs into a single (named) *RDF graph merge*." I hope I can provide some test cases/examples that back that up before the next TC. cheers, Axel On 18 Feb 2011, at 21:31, Axel Polleres wrote: > Hi all, > > Alex and I took a stab on the formal semantics these last few days [1], and indeed I now > realize that we missed out the resolution about blank nodes in DELETE templates acting as > "wild cards"[2] (although that omission was mentioned in my original review :-) we simply > forgot it). > > However, there's a mostly straightforward fix to this, I believe, see below. > If agreeable, I can work this into the spec, together with Alex. > > best, > Axel > > =========================================================================== > > Take the definition of OpDeleteInsert [3] > ----------------------------------------------- > OpDeleteInsert(GS, modify_template_DEL, modify_template_INS, P) = Dataset-UNION(Dataset-DIFF(GS, Dataset(modify_templateDEL,P)), Dataset(modify_templateINS, P)) > ----------------------------------------------- > > This needs to be modified as follows: > > ----------------------------------------------- > OpDeleteInsert(GS, modify_template_DEL, modify_template_INS, P) = Dataset-UNION(Dataset-DIFF(GS, Dataset(modify_templateDEL',P')), Dataset(modify_templateINS, P)) > ----------------------------------------------- > > where modify_template_DEL' and P' are obtained by the following preprocessing step: > > For any unnamed bnode _:B in a modify_template_DEL > (i) new variables ?Var_B ?Var_B1 ?Var_B2 ?Var_Bg are introduced, > (ii) _:B is replaced by ?Var_B in a modify_template_DEL, > (iii) Pattern P is replaced by P_B such that > > P_B = { P } UNION { > SELECT DISTINCT ?Var_B > { { ?Var_B ?Var_B1 ?Var_B2 } UNION > { ?Var_B1 ?Var_B ?Var_B2 } UNION > { ?Var_B1 ?Var_B2 ?Var_B } UNION > { GRAPH ?Var_Bg {?Var_B1 ?Var_B2 ?Var_B } } UNION > { GRAPH ?Var_Bg {?D1 ?Var_B2 ?Var_B } } UNION > { GRAPH ?Var_Bg {?Var_B1 ?Var_B2 ?Var_B } } } > > That is, ?Var_B binds to all possible values in the vocabulary of GS. > > Then, modify_template_DEL', and P', respectively, denote the modify_template > and pattern obtained by applying this rewriting repeatedly for any bnode > in modify_template_DEL and starting with the original pattern P. > > > I know that the definition of P_B doesn't look very nice, but this definition should cover the intended semantics of [2]. > In principle, the idea is that bnodes, that should behave as wildcard should bind to *any* element in the signature of GS, > which is what is returned by the subquery > Q = SELECT DISTINCT ?D > { { ?D ?D1 ?D2 } UNION > { ?D1 ?D ?D2 } UNION > { ?D1 ?D2 ?D } UNION > { GRAPH ?Dg {?D1 ?D2 ?D } } UNION > { GRAPH ?Dg {?D1 ?D2 ?D } } UNION > { GRAPH ?Dg {?D1 ?D2 ?D } } } > > > Alternatively, (which might be more elegant, but I can't really get my head around it this hour of the day) > we could define the behaviour more semantically, instead of rewriting P, by joining the pattern solutions for P with a > "universal binding" Omega_U(Var) = { (?X , term) | term in signature(GS) }. It should be obvious, that Q returns exactly Omega_U(?D). > > So, summarising, I obviously mean by no means to suggest that this is a way to *implement* the feature, but it doesn't seem to be a big deal > at all to refine the semantics to cater for the behavior given in the resolution, all is needed is a modification of OpDeleteInsert. > > best, > Axel > > > 1. http://www.w3.org/2009/sparql/docs/update-1.1/Overview.xml#formalModelGraphUpdate > 2. http://www.w3.org/2009/sparql/meeting/2010-03-09#resolution_2 > 3. http://www.w3.org/2009/sparql/docs/update-1.1/Overview.xml#def_deleteinsertoperation
Received on Friday, 18 February 2011 21:47:53 UTC