SPARQL subqueries

This style of subqueries will also work (you can do this one without a subquery too, but it’s just an example of course):

SELECT ?name COUNT(?msg)
	?from a nco:Contact  ;
	          nco:hasEmailAddress ?name . {
		SELECT ?from
			?msg a nmo:Email ;
			         nmo:from ?from .
} GROUP BY ?from  

The same query in QtTracker will look like this (I have not tested this, let me know if it’s wrong Iridian):

#include <QObject>
#include <QtTracker/Tracker>
#include <QtTracker/ontologies/nco.h>
#include <QtTracker/ontologies/nmo.h>

void someFunction () {
	RDFSelect outer;
	RDFVariable from;
	RDFVariable name = outer.newColumn<nco::Contact>("name");
	RDFSelect inner = outer.subQuery();
	RDFVariable in_from = inner.newColumn("from");
	RDFVariable msg;<nmo::from>(in_from);
	outer.addCountColumn("total messages", msg);
	LiveNodes from_and_count = ::tracker()->modelQuery(outer);

What you find in this branch already supports it. You can find early support for subqueries in QtTracker in this branch.

To quickly put some stuff about Emails into your RDF store, read this page (copypaste the turtle examples in a file and use the tracker-import tool). You can also enable our Evolution Tracker plugin, of course.

ps. Yes, somebody should while building a GLib/GObject based client library for Tracker copy ideas from QtTracker.

4 thoughts on “SPARQL subqueries”

  1. Thanks for pointing out that library, I indeed forgot to mention it. I turned some text in the blog into a link to it. The sparql-glib library of course doesn’t support subqueries yet. Let’s see if we can help the sparql-glib people implementing that …

  2. @Jos: There’s a script that you can run. The README file of QtTracker explains it. It also works on custom ontologies that you install into Tracker. But note that we don’t yet officially support custom ontologies as a feature (you right now have to destroy your database to install one, in future we’ll allow you to install one at any time).

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