ParameterizedSparqlString does not work either (not related to bnodes).
With a mapping ?minCount => 0, it produces an invalid query string:
SELECT (count(*) AS ?cardinality)
WHERE
{ <http://spinrdf.org/spin#Templates>
<http://spinrdf.org/spin#body> ?value
FILTER bound(0)
}
HAVING ( ?cardinality < 0 )
On Sun, Jul 5, 2020 at 10:31 PM Andy Seaborne <a...@apache.org> wrote:
>
>
>
> On 05/07/2020 20:36, Martynas Jusevičius wrote:
> > Thanks for the explanation.
> >
> > What do you mean with "inject" in 1/? ParameterizedSparqlString?
>
> initialBinding is done by making the starting condition for execution a
> binding of the variables instead of the empty root. (This works nearly
> always but is affected by variable name scopes - scopes, like subquery,
> didn't exist when the mechanism was introduced.
>
> ParameterizedSparqlString builds which is parsed so you should be able
> to put in <_:....>.
>
> Andy
>
> >
> > On Sun, Jul 5, 2020 at 8:53 PM Andy Seaborne <a...@apache.org> wrote:
> >>
> >> <_:label> is a syntax feature, not built into the storage or query
> >> execution.
> >>
> >> model.createResource("_:" + id));
> >>
> >> creates a resource with a strange URI (which is actually illegal by RFC
> >> 3986/7).
> >>
> >> There are various ways:
> >>
> >> 1/ The app can put the bnode into the QSM and injected at execution - it
> >> won't become a bnode-variable because that happens in parsing.
> >>
> >> 2/ To put a concrete node into a query:
> >>
> >> String bn = "<_:" + id+">";
> >>
> >> then put string into SPARQL syntax:
> >>
> >> QueryFactory.create("SELECT * { VALUES ?s {"+bn+"} ?s ?p ?o }");
> >> QueryFactory.create("SELECT * { "+bn+" ?p ?o }");
> >>
> >> 3/ rewrite the abstract syntax after parsing:
> >>
> >> Map<String, Resource> substitutions =
> >> Collections.singletonMap("s", bnode);
> >> query = QueryFactory.create("SELECT * { ?s ?p ?o }");
> >> query = QueryTransformOps.transformQuery(query, substitutions);
> >>
> >> Forms 2 and 3 have the advantage of not relying on how execution works -
> >> QSMs are ingested inthe start of execution and e.g. aren't visible in
> >> subqueries and also interact and bypass with query optimization.
> >>
> >> Andy
> >>
> >> On 05/07/2020 15:22, Martynas Jusevičius wrote:
> >>> Hi,
> >>>
> >>> I came across a situation where I want to carry over a blank node ID
> >>> in a QuerySolutionMap to QueryExecution, to match exact blank node
> >>> resources rather than have them as variables.
> >>>
> >>> I found an old thread by Holger on this topic:
> >>> https://mail-archives.apache.org/mod_mbox/jena-users/201308.mbox/browser
> >>>
> >>> The suggestion was to use <_:LABEL> URI scheme for blank nodes.
> >>> https://jena.apache.org/documentation/query/extension.html#blank-node-labels
> >>>
> >>> Based on that, I tried this logic:
> >>>
> >>> if (instance.isURIResource()) qsm.add(SPIN.THIS_VAR_NAME, instance);
> >>> if (instance.isAnon()) qsm.add(SPIN.THIS_VAR_NAME,
> >>> model.createResource("_:" + instance.getId()));
> >>>
> >>> However I'm not getting the results I expect. So I decided to make an
> >>> isolated test:
> >>>
> >>> @Test
> >>> public void bnodeQueryTest()
> >>> {
> >>> Model model = ModelFactory.createDefaultModel();
> >>> Resource bnode = model.createResource().addProperty(FOAF.name,
> >>> "whateverest");
> >>> AnonId id = bnode.getId();
> >>>
> >>> Query query = QueryFactory.create("SELECT * { ?s ?p ?o }");
> >>> QuerySolutionMap qsm = new QuerySolutionMap();
> >>> qsm.add("s", model.createResource("_:" + id));
> >>>
> >>> try (QueryExecution qex = QueryExecutionFactory.create(query,
> >>> model, qsm))
> >>> {
> >>> ResultSet resultSet = qex.execSelect();
> >>>
> >>> assertTrue(resultSet.hasNext());
> >>> assertEquals(id,
> >>> resultSet.next().get("s").asResource().getId());
> >>> }
> >>> }
> >>>
> >>> The test fails on assertTrue() because SELECT returns no results.
> >>>
> >>> Is the test flawed? Am I misunderstanding the use of this URI scheme?
> >>> If not, what's the purpose if it cannot match blank nodes in data?
> >>>
> >>> Martynas
> >>>
