On 01/03/2020 17:06, Steve Vestal wrote:
I am using the results of one SPARQL query against an OntModel to
construct follow-on SPARQL queries. The OntModel contains blank nodes
to denote some classes and individuals. QueryResult gives me RDFNodes,
and I am using methods such as RDFNode#as(Class<T>) to obtain more
specific classifications for nodes including blank nodes (which seems to
work). My understanding is that this gives me a Resource in the context
of the original, queried OntModel.
>
I am currently creating textual SPARQL queries. My first question is,
what is the recommended way to represent a blank node in a textual
SPARQL query? Is something like the following a reliable thing to do?
if (rdfNode.isAnon()) then {subjectName = "<" +
rdfNode.asResource().getId().getLabelString() + ">";}
It depends on how you are accessing the data.
If you have a same-JVM model (in-memory or TDB) as in your previous emails:
In a query string, or parameterized query string, use a URI starting "_:"
"<_:" +
rdfNode.asResource().getId().getLabelString() +
">"
-------------------
If using Fuseki:
In the client, use RDFConnectionFactory.connectFuseki
OR
start the server with Context setting : arq:outputGraphBNodeLabels=true
causes blank nodes to come back with internal ids.
--set arq:outputGraphBNodeLabels=true
and in the client:
--set arq:inputGraphBNodeLabels=true
and use <_:...> in query strings.
My second question deals with the case where the initial SPARQL query is
a CONSTRUCT rather than a SELECT query, which returns a Model. What is
the relationship between blank nodes in the constructed Model and the
OntModel that was initially queried? If I visit triples using a
StmtIterator over the constructed Model, and create a textual name for a
blank node as above, can that name be used in a query applied to the
original OntModel? How do I make sure that a blank node found in the
constructed Model will be mapped to the corresponding blank node in the
originating OntModel?
When the data is same-JVM, it will be the same blank node as the data.
The OntModel API works.
Use the Resource object from QuerySolution::geResource.
You don't need to create a string.
(Blank nodes have global system identifiers)
----------------------
Note about blank nodes:
If you find yourself using the blank nodes resources a lot and can
change the data, then change the data to use a URI, even if one like
<urn:uuid:...>
Blank nodes being blank are saying "you don't need the name - find it in
the graph each time".
Andy
