good evening; > On 2016-11-01, at 20:12, Andy Seaborne <a...@apache.org> wrote: > > > > On 01/11/16 12:38, Osma Suominen wrote: >> Hi, >> [about a query which exercises the interaction between a values clause and >> statement pattern at locations relatively remote in the query. ] > > [ the question leads to a point about the scope of the respective ?uri > variables, ] > > The issue is [*], using the variable ?uri again inside an OPTIONAL. > > It is possible that ?uri will range over more than the VALUES setting and > affect the OPTIONAL yet the inner EXISTS usage does not set ?uri and it is > not propagated to be joined with the set value. > > […] > > [ … and to one about algebraic equivalence among expressions and the > consequent latitude to relocate the values clause.] > > It can be pushed in because: > > join(A, union(B,C)) == union(join(A,B), join(A,C)) > > now if A is an complex expression, that is a bad idea (probably). > > If A is a small VALUES block then it makes sense. It isn't done though. >
both of which are significant, but remain side matters to the principal issue, which concerns a reasonable expectation - despite that it may be subject to revision, that the values clause introduces bindings with indefinite scope.[1] as sparql plays in increasingly significant role in service implementations, library-level support for query parameters[2] needs to give way to protocol-level mechanisms,[3] whereby the language semantics needs more attention than it has yet received. both immediately federated request combinations and request chains which are mediated by a third service need to propagate intermediate solution sets across requests. the use case behind this question is one example. the implementations for elementary variables[3] do not provide sufficient capacity - not to mention the deficiencies of their substitution models. the sparql federated query recommendation suggests a role which the values clause might play,[4] but does not provide an exact interpretation. has jena’s community given this topic any thought? best regards, from berlin, - - - [1] : http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node43.html#SECTION00700000000000000000 [2] : https://jena.apache.org/documentation/query/parameterized-sparql-strings.html [3] : http://docs.rdf4j.org/rest-api/#_repository_queries [4] : http://www.w3.org/TR/sparql11-federated-query/#values --- james anderson | ja...@dydra.com | http://dydra.com
