SPARQL Query

This node can be connected with Semantic Web endpoints to perform SELECT queries. Please note that based on the connected endpoint, same data and same queries may lead to different results. For instance, the following SELECT query

SELECT * WHERE {?s ?p ?o}

queries all triples in the default graph, if an In-Memory Endpoint is connected. A Virtuoso database (by Virtuoso Endpoint ) will reutrn all triples present in the database.
To query specific graphs, e.g. graphs named a and b, the query with an In-Memory Endpoint is

SELECT * WHERE { { GRAPH <a> { ?s ?p ?o } } UNION { GRAPH <b> { ?s ?p ?o } } }

But with a Virtuoso database it is

SELECT * FROM NAMED <a> FROM NAMED <b> WHERE { GRAPH ?graph { ?s ?p ?o } }

The N-Triples format for the query result is necessary to be kept if you want to insert the triples in an endstore. This is especially imporant for (typed) literals. If the N-Triples format is not preserved type information will get lost (a String representation of the literal is returned). For URIs the angled brackets are not preserved, which are necessary for insertion. Here is an example showing triples with and without format preservation:

Preserve	sub	pred	object
Yes	<http://expl.org/expl>	<http://expl.org/integer>	4
No	http://expl.org/expl	http://expl.org/integer	4
Yes	<http://expl.org/expl>	<http://expl.org/string>	"4"
No	http://expl.org/expl	http://expl.org/string	4
Yes	<http://expl.org/expl>	<http://expl.org/string>	"sometstring"@en
No	http://expl.org/expl	http://expl.org/string	sometstring
Yes	<http://expl.org/expl>	<http://expl.org/own>	"123k"^^<http://expl.org/owntype>
No	http://expl.org/expl	http://expl.org/own	123k

Functionality is provided using the Apache Jena Framework

Input ports

1. Type: Semantic Web Connection
   Semantic Web Connection
   Semantic Web connection

Output ports

1. Type: Table
   Query Result Table
   Buffered Data Table containing query results