relpipe-data/examples-rdf-sparql.xml
author František Kučera <franta-hg@frantovo.cz>
Mon, 21 Feb 2022 00:43:11 +0100
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<stránka
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	xmlns="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/strana"
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	xmlns:m="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/makro">
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	<nadpis>Querying an RDF triplestore using SPARQL</nadpis>
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	<perex>use SQL-DK with Jena JDBC driver or a custom script to gather linked data</perex>
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	<m:pořadí-příkladu>04300</m:pořadí-příkladu>
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	<text xmlns="http://www.w3.org/1999/xhtml">
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		<p>
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			In the Resource Description Framework (<a href="https://www.w3.org/RDF/">RDF</a>) world, there are no relations.
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			The data model is quite different.
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			It is built on top of triples: subject – predicate – object.
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			Despite there are no tables (compared to relational databases), RDF is not a schema-less clutter – 
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			actually RDF has a schema (ontology, vocabulary), just differently shaped.
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			Subjects and predicates are identified by <a href="https://en.wikipedia.org/wiki/Internationalized_Resource_Identifier">IRI</a>s
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			(or formerly <a href="https://en.wikipedia.org/wiki/Uniform_Resource_Identifier">URI</a>s)
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			that are globally unique (compared to primary keys in relational databases that are almost never globally unique).
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			Objects are also identified by IRIs (and yes, one can be both subject and object) or they can be a primitive values like a text string or a number.
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		</p>
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		<m:diagram orientace="vodorovně">
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			node [fontname = "Latin Modern Sans, sans-serif"];
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			edge [fontname = "Latin Modern Sans, sans-serif"];
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			subject	->	object [ label = "predicate"];
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		</m:diagram>
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		<p>
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			This <em>triple</em> is also called a <em>statement</em>.
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			In the following statement:
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		</p>
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		<blockquote>
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			<m:name/> tools are released under the GNU GPL license.
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		</blockquote>
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		<p>we recognize:</p>
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		<ul>
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			<li>
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				Subject: <i>					
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					<m:name/> tools</i>
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			</li>
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			<li>Predicate: <i>is released under license</i></li>
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			<li>Object: <i>GNU GPL</i></li>
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		</ul>
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		<p>
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			This data model is seemingly simple: just a graph, two kinds of nodes and edges connecting them together.
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			Or a flat list of statements (triples).
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			But it can be also very complicated, depending on how we use it and how rich ontologies we design.
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			RDF can be studied for years and is a great topic for diploma thesis and dissertations,
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			but in this example, we will keep it as simple as possible.
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		</p>
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		<p>
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			Collections of statements are stored in special databases called triplestores.
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			The data inside can be queried using the 
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			<a href="https://www.w3.org/TR/sparql11-overview/">SPARQL</a> language through the endpoint provided by the triplestore.
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			Popular implementations are 
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			<a href="https://jena.apache.org/">Jena</a>,
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			<a href="http://vos.openlinksw.com/owiki/wiki/VOS">Virtuoso</a> and
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			<a href="https://rdf4j.org/about/">RDF4J</a>
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			(all free software).
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		</p>
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		<p>
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			Relational model can be easily mapped to RDF.
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			We can just simply add a prefix to the primary keys to make them globally unique IRIs.
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			The attributes will become predicates (also prefixed).
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			And the values will become objects (either primitive values or IRIs in case of foreign keys).
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			Of course, more complex transformation can be done – this is the most straightforward way.
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		</p>
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		<p>
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			Mapping RDF data to relational model is bit more difficult.
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			Sometimes easy, sometimes very cumbersome.
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			We can always design some kind of EAV (entity – attribute – value) model in the relational database
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			or we can create a relation for each predicate…
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			If we do some universal automatic mapping and retain the flexibility of RDF and richness of the original ontology,
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			we usually lose the performance and simplicity of our relational queries.
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			Good mapping that will feel natural and idiomatic in the relational world and will perform well usually poses some hard work.
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		</p>
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		<p>
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			But mapping mere results of a SPARQL query obtained from an RDF endpoint is a different story.
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			These results can be seen as records and processed using our relational tools,
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			stored, transformed or converted to other formats, displayed in GUI windows or safely passed to shell scripts.
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			This example shows how we can bridge the RDF and relational worlds.
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		</p>
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		<h2>Several ways of connecting to an RDF triplestore</h2>
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		<p>
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			Currently there is no official <code>relpipe-in-rdf</code> or <code>relpipe-in-sparql</code> tool.
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			It will be probably part of some future release of <m:name/>.
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			But until then, despite this lack, we still have several options how to join the RDF world
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			and let the data from an RDF triplestore flow through our relational pipelines:
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		</p>
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		<ul>
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			<li>SQL-DK + Jena JDBC driver + <code>relpipe-in-xml</code></li>
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			<li>ODBC-JDBC bridge + Jena JDBC driver + <code>relpipe-in-sql</code></li>
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			<li>A native SPARQL ODBC driver + <code>relpipe-in-sql</code></li>
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			<li>A shell script + <code>relpipe-in-csv</code> or <code>relpipe-in-xml</code></li>
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		</ul>
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		<p>In this example, we will look at the first and the last option.</p>
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		<h2>SQL-DK + Jena JDBC driver</h2>
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		<p>
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			Apache Jena is not only a triplestore,
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			it is a framework consisting of several parts
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			and provides also a special JDBC driver that is ready to use
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			(despite this <a href="https://issues.apache.org/jira/browse/JENA-1939">small bug</a>).
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			Thanks to this driver, we can use existing Java tools and run SPARQL queries instead of SQL ones.
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		</p>
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		<p>
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			Such a tool that uses this standard API (JDBC)
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			is <a href="https://sql-dk.globalcode.info/">SQL-DK</a>.
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			This tool integrates well with <m:name/> because it can output results in the XML format (or alternatively the Recfile format)
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			that can be directly consumed by <code>relpipe-in-xml</code> (or alternatively <code>relpipe-in-recfile</code>).
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		</p>
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		<p>First we download Jena source codes:</p>
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		<m:pre jazyk="bash"><![CDATA[mkdir -p ~/src; cd ~/src
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git clone https://gitbox.apache.org/repos/asf/jena.git]]></m:pre>
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		<p>
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			and apply the <a href="https://git-zaloha.frantovo.cz/gitbox.apache.org/repos/asf/jena.git/commit/?h=JENA-1939_updateCount&amp;id=bdb5439d22b80b2909258449d82fb7b5003fd64c">patch</a>
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			for abovementioned bug (if not already merged in the upstream).
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		</p>
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		<p>n.b. As always when doing such experiments, we would probably run this under a separate user account or in a virtual machine.</p>
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		<p>Then we will compile the JDBC driver:</p>
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		<m:pre jazyk="bash"><![CDATA[cd ~/src/jena/jena-jdbc/
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mvn clean install]]></m:pre>
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		<p>
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			Now we will install SQL-DK (either from sources or from <code>.deb</code> or <code>.rpm</code> package)
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			and run it for the first time (which creates the configuration directory and files):
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		</p>
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		<pre>sql-dk --list-databases</pre>
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		<p>Then we will register the previously compiled Jena JDBC driver in the <code>~/.sql-dk/environment.sh</code></p>
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		<m:pre jazyk="bash"><![CDATA[CUSTOM_JDBC=(
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	~/src/jena/jena-jdbc/jena-jdbc-driver-bundle/target/jena-jdbc-driver-bundle-*.jar
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);]]></m:pre>
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		<p>And we should see it among other drivers:</p>
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		<pre><![CDATA[$ sql-dk --list-jdbc-drivers 
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 ╭──────────────────────────────────────────────────┬───────────────────┬─────────────────┬─────────────────┬──────────────────────────╮
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 │ class                                  (VARCHAR) │ version (VARCHAR) │ major (INTEGER) │ minor (INTEGER) │ jdbc_compliant (BOOLEAN) │
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 ├──────────────────────────────────────────────────┼───────────────────┼─────────────────┼─────────────────┼──────────────────────────┤
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 │ org.postgresql.Driver                            │ 9.4               │               9 │               4 │                    false │
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 │ com.mysql.jdbc.Driver                            │ 5.1               │               5 │               1 │                    false │
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 │ org.sqlite.JDBC                                  │ 3.25              │               3 │              25 │                    false │
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 │ org.apache.jena.jdbc.mem.MemDriver               │ 1.0               │               1 │               0 │                    false │
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 │ org.apache.jena.jdbc.remote.RemoteEndpointDriver │ 1.0               │               1 │               0 │                    false │
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 │ org.apache.jena.jdbc.tdb.TDBDriver               │ 1.0               │               1 │               0 │                    false │
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 ╰──────────────────────────────────────────────────┴───────────────────┴─────────────────┴─────────────────┴──────────────────────────╯
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Record count: 6]]></pre>
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		<p>The driver seems present so we can configure the connection in the <code>~/.sql-dk/config.xml</code> file:</p>
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		<m:pre jazyk="xml"><![CDATA[<database>
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	<name>rdf-dbpedia</name>
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	<url>jdbc:jena:remote:query=http://dbpedia.org/sparql</url>
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	<userName></userName>
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	<password></password>
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</database>]]></m:pre>
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		<p>
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			This will connect us to the DBpedia endpoint (more datasources are mentioned in the chapter below).
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			We can test the connection:
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		</p>
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		<pre><![CDATA[$ sql-dk --test-connection rdf-dbpedia 
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 ╭─────────────────────────┬──────────────────────┬─────────────────────┬────────────────────────┬───────────────────────────╮
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 │ database_name (VARCHAR) │ configured (BOOLEAN) │ connected (BOOLEAN) │ product_name (VARCHAR) │ product_version (VARCHAR) │
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 ├─────────────────────────┼──────────────────────┼─────────────────────┼────────────────────────┼───────────────────────────┤
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 │ rdf-dbpedia             │                 true │                true │                        │                           │
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 ╰─────────────────────────┴──────────────────────┴─────────────────────┴────────────────────────┴───────────────────────────╯
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Record count: 1]]></pre>
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		<p>and run our first SPARQL query:</p>
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		<pre><![CDATA[$ sql-dk --db rdf-dbpedia --formatter tabular-prefetching --sql "SELECT * WHERE { ?subject ?predicate ?object . } LIMIT 8"
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 ╭──────────────────────────────────────────────────────────────────────────────┬─────────────────────────────────────────────────┬─────────────────────────────────────────────────────────╮
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 │ subject                                         (org.apache.jena.graph.Node) │ predicate          (org.apache.jena.graph.Node) │ object                     (org.apache.jena.graph.Node) │
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 ├──────────────────────────────────────────────────────────────────────────────┼─────────────────────────────────────────────────┼─────────────────────────────────────────────────────────┤
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 │ http://www.openlinksw.com/virtrdf-data-formats#default-iid                   │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 │ http://www.openlinksw.com/virtrdf-data-formats#default-iid-nullable          │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 │ http://www.openlinksw.com/virtrdf-data-formats#default-iid-nonblank          │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 │ http://www.openlinksw.com/virtrdf-data-formats#default-iid-nonblank-nullable │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 │ http://www.openlinksw.com/virtrdf-data-formats#default                       │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 │ http://www.openlinksw.com/virtrdf-data-formats#default-nullable              │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 │ http://www.openlinksw.com/virtrdf-data-formats#sql-varchar                   │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 │ http://www.openlinksw.com/virtrdf-data-formats#sql-varchar-nullable          │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://www.openlinksw.com/schemas/virtrdf#QuadMapFormat │
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 ╰──────────────────────────────────────────────────────────────────────────────┴─────────────────────────────────────────────────┴─────────────────────────────────────────────────────────╯
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Record count: 8]]></pre>
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		<p>
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			Not a big fun yet, but it proves that the connection is working and we are getting some results from the endpoint.
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			We will run some more interesting queries later.
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		</p>
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		<p>
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			When we switch to the <code>--formatter xml</code> we can pipe the stream from SQL-DK
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			to <code>relpipe-in-xml</code> and then process it using relational tools.
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			We can also use the <code>--sql-in</code> option of SQL-DK which reads the query from STDIN (instead of from command line argument)
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			and then wrap it as a reusable script that reads SPARQL and outputs relational data:
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		</p>
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		<m:pre jazyk="bash">sql-dk --db "rdf-dbpedia" --formatter "xml" --sql-in | relpipe-in-xml</m:pre>
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		<p>
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			For accessing remote SPARQL endpoint this is a bit overkill with lot of dependencies (so we will use different approach in the next chapter).
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			But Jena JDBC driver is not only for accessing remote endpoints – we can use it as an embedded database,
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			either an in-memory one or regular DB backed by persistent files.
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		</p>
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		<p>
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			The in-memory database loads some initial data and then operates on them.
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			So we configure such connection:
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		</p>
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		<m:pre jazyk="xml"><![CDATA[<database>
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	<name>rdf-in-memory</name>
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	<url>jdbc:jena:mem:dataset=/tmp/rdf-initial-data.ttl</url>
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	<userName></userName>
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	<password></password>
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</database>]]></m:pre>
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		<p>It runs fine, but <a href="https://en.wikipedia.org/wiki/Turtle_(syntax)">turtles</a> are not at home:</p>
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		<pre><![CDATA[$ echo > /tmp/rdf-initial-data.ttl
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$ echo "SELECT * WHERE { ?subject ?predicate ?object . }" | sql-dk --db rdf-in-memory --formatter tabular-prefetching --sql-in 
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 ╭──────────────────────────────────────┬────────────────────────────────────────┬─────────────────────────────────────╮
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 │ subject (org.apache.jena.graph.Node) │ predicate (org.apache.jena.graph.Node) │ object (org.apache.jena.graph.Node) │
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 ├──────────────────────────────────────┼────────────────────────────────────────┼─────────────────────────────────────┤
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 ╰──────────────────────────────────────┴────────────────────────────────────────┴─────────────────────────────────────╯
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Record count: 0]]></pre>
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		<p>
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			If we are in a desperate need of turtles and have installed any <a href="https://lv2plug.in/">LV2</a> plugins,
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			we can find some and put them in our initial data file or reconfigure the database connection:
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		</p>
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		<pre><![CDATA[$ find /usr/lib -name '*.ttl' | head
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/usr/lib/lv2/fil4.lv2/manifest.ttl
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/usr/lib/lv2/fil4.lv2/fil4.ttl
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/usr/lib/ardour5/LV2/a-fluidsynth.lv2/manifest.ttl
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/usr/lib/ardour5/LV2/a-fluidsynth.lv2/a-fluidsynth.ttl
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/usr/lib/ardour5/LV2/reasonablesynth.lv2/manifest.ttl
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/usr/lib/ardour5/LV2/reasonablesynth.lv2/reasonablesynth.ttl
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/usr/lib/ardour5/LV2/a-delay.lv2/manifest.ttl
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/usr/lib/ardour5/LV2/a-delay.lv2/presets.ttl
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/usr/lib/ardour5/LV2/a-delay.lv2/a-delay.ttl
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/usr/lib/ardour5/LV2/a-eq.lv2/manifest.ttl
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$ cat /usr/lib/lv2/fil4.lv2/manifest.ttl > /tmp/rdf-initial-data.ttl
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$ sed s@/tmp/rdf-initial-data.ttl@/usr/lib/lv2/fil4.lv2/manifest.ttl@g -i ~/.sql-dk/config.xml]]></pre>
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		<p>and look through Jena/RDF/SPARQL what is inside:</p>
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		<pre><![CDATA[$ echo "SELECT * WHERE { ?subject ?predicate ?object . }" | sql-dk --db rdf-in-memory --formatter xml --sql-in | relpipe-in-xml | relpipe-out-tabular 
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r1:
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 ╭───────────────────────────────────────┬─────────────────────────────────────────────────┬───────────────────────────────────────────╮
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 │ subject                      (string) │ predicate                              (string) │ object                           (string) │
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 ├───────────────────────────────────────┼─────────────────────────────────────────────────┼───────────────────────────────────────────┤
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 │ http://gareus.org/oss/lv2/fil4#ui_gl  │ http://www.w3.org/2000/01/rdf-schema#seeAlso    │ file:///usr/lib/lv2/fil4.lv2/fil4.ttl     │
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 │ http://gareus.org/oss/lv2/fil4#ui_gl  │ http://lv2plug.in/ns/extensions/ui#binary       │ file:///usr/lib/lv2/fil4.lv2/fil4UI_gl.so │
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 │ http://gareus.org/oss/lv2/fil4#ui_gl  │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://lv2plug.in/ns/extensions/ui#X11UI  │
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 │ http://gareus.org/oss/lv2/fil4#mono   │ http://www.w3.org/2000/01/rdf-schema#seeAlso    │ file:///usr/lib/lv2/fil4.lv2/fil4.ttl     │
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 │ http://gareus.org/oss/lv2/fil4#mono   │ http://lv2plug.in/ns/lv2core#binary             │ file:///usr/lib/lv2/fil4.lv2/fil4.so      │
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 │ http://gareus.org/oss/lv2/fil4#mono   │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://lv2plug.in/ns/lv2core#Plugin       │
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 │ http://gareus.org/oss/lv2/fil4#stereo │ http://www.w3.org/2000/01/rdf-schema#seeAlso    │ file:///usr/lib/lv2/fil4.lv2/fil4.ttl     │
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 │ http://gareus.org/oss/lv2/fil4#stereo │ http://lv2plug.in/ns/lv2core#binary             │ file:///usr/lib/lv2/fil4.lv2/fil4.so      │
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 │ http://gareus.org/oss/lv2/fil4#stereo │ http://www.w3.org/1999/02/22-rdf-syntax-ns#type │ http://lv2plug.in/ns/lv2core#Plugin       │
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 ╰───────────────────────────────────────┴─────────────────────────────────────────────────┴───────────────────────────────────────────╯
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Record count: 9]]></pre>
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		<p>
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			Now we can be sure that LV2 uses the Turtle format for plugin configurations,
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			which is quite ingenious and inspirational – 
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			such configuration is well structured and its options (predicates in general) have globally unique identifiers (IRIs).
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			Also plugins are identified by IRIs which is great, because it avoids name collisions.
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		</p>
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312
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		<p id="turtle">
310
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			Let us make some own turtles.
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			Reconfigure the database connection back:
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		</p>
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		<pre>sed s@/usr/lib/lv2/fil4.lv2/manifest.ttl@/tmp/rdf-initial-data.ttl@g -i ~/.sql-dk/config.xml</pre>
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		<p>and fill the <code>/tmp/rdf-initial-data.ttl</code> with some new data:</p>
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		<m:pre jazyk="turtle"><![CDATA[<http://example.org/person/you>
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	<http://example.org/predicate/have>
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	<http://example.org/thing/nice-day> .]]></m:pre>
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		<p>
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			Turtle is a simple format that contains statements.
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			Subjects, predicates and objects are separated by spaces (tabs and line-ends are here just to make it more readable for us).
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			And statements end with <i>full stop</i> like ordinary sentences.
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		</p>
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		<p>
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			To avoid repeating common parts of IRIs we can declare namespace prefixes:
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		</p>
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		<m:pre jazyk="turtle"><![CDATA[@prefix person:     <http://example.org/person/> .
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@prefix predicate:  <http://example.org/predicate/> .
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@prefix thing:      <http://example.org/thing/> .
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person:you
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	predicate:have
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		thing:nice-day .]]></m:pre>
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		<p>
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			This format is very concise.
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			If we describe the same subject, we use <i>semicolon</i> to avoid repeating it.
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			And if even the predicate is the same (multiple values), we use <i>comma</i>:
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		</p>
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		<m:pre jazyk="turtle"><![CDATA[@prefix person:     <http://example.org/person/> .
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@prefix predicate:  <http://example.org/predicate/> .
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@prefix thing:      <http://example.org/thing/> .
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person:you
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	predicate:have
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		thing:nice-day, thing:much-fun;
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	predicate:read-about
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		thing:relational-pipes .]]></m:pre>
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		<p>
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			Jena will parse our file and respond to our basic query with these data:
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		</p>
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		<pre><![CDATA[$ echo "SELECT * WHERE { ?subject ?predicate ?object . }" | sql-dk --db rdf-in-memory --formatter xml --sql-in --relation rdf_results | relpipe-in-xml | relpipe-out-tabular 
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rdf_results:
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 ╭───────────────────────────────┬─────────────────────────────────────────┬───────────────────────────────────────────╮
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 │ subject              (string) │ predicate                      (string) │ object                           (string) │
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 ├───────────────────────────────┼─────────────────────────────────────────┼───────────────────────────────────────────┤
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 │ http://example.org/person/you │ http://example.org/predicate/read-about │ http://example.org/thing/relational-pipes │
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 │ http://example.org/person/you │ http://example.org/predicate/have       │ http://example.org/thing/much-fun         │
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 │ http://example.org/person/you │ http://example.org/predicate/have       │ http://example.org/thing/nice-day         │
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 ╰───────────────────────────────┴─────────────────────────────────────────┴───────────────────────────────────────────╯
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Record count: 3]]></pre>
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		<p>Or if we prefer more vertical formats like Recfile:</p>
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		<pre><![CDATA[$ echo "SELECT * WHERE { ?subject ?predicate ?object . }" | sql-dk --db rdf-in-memory --formatter xml --sql-in --relation rdf_results | relpipe-in-xml | relpipe-out-recfile 
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%rec: rdf_results
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subject: http://example.org/person/you
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predicate: http://example.org/predicate/read-about
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object: http://example.org/thing/relational-pipes
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subject: http://example.org/person/you
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predicate: http://example.org/predicate/have
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object: http://example.org/thing/much-fun
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subject: http://example.org/person/you
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predicate: http://example.org/predicate/have
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object: http://example.org/thing/nice-day]]></pre>
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		<p>Let us create some more data:</p>
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		<m:pre jazyk="turtle" src="examples/rdf-heathers.ttl"/>
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		<p>list them as statements:</p>
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		<m:pre jazyk="text" src="examples/rdf-heathers.txt"/>
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		<p>and run some more SPARQL queries…</p>
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		<p>
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			Note:
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			<em>
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				we use <a href="https://tools.ietf.org/html/rfc4151">The tag: URI scheme</a> for our IRIs.
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				It makes URIs (IRIs) globally unique not only in space but also in time (domain owners change during time).
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				Which is great.
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				In the semantic web and linked data world, it is not common and locators (URLs) are used rather than pure identifiers (URIs, IRIs).
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				But here we want to emphasise that we work strictly with our local data
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				and make it clear that we do not depend on any on-line resources and nothing will be downloaded from remote servers.
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				And in a real project, we should use existing ontologies / vocabularies as much as possible instead of inventing new ones.
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				But we keep this example rather isolated from the complexity of the outer world and bit synthetic.
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			</em>
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		</p>
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		<p>Find all quotes and names of their authors:</p>
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		<m:sparql-example name="examples/rdf-heathers-quotes"/>
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		<p>List groups and counts of their members:</p>
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		<m:sparql-example name="examples/rdf-heathers-members"/>
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		<p>Filter by a regular expression and list actor names rather than characters:</p>
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		<m:sparql-example name="examples/rdf-heathers-much"/>
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		<p>Now imagine semantic model of Twin Peaks… How very!</p>
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		<h2>Improvised relpipe-in-sparql tool</h2>
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		<p>
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			Starting the JVM and creating always a new database from scratch on each query is quite… <i>heavy</i>.
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			We can keep Jena running in the background and connect to its SPARQL endpoint – or connect to any other endpoint on the internet.
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			So we will hack together a light script and name it <code>relpipe-in-sparql</code> (in some future release there will be such official tool).
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		</p>
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		<p>
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			Because SPARQL endpoints accept plain HTTP requests, support besides XML also CSV and we already have <code>relpipe-in-csv</code>
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			the script can be very simple:
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   427
		</p>
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   428
		
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parents:
diff changeset
   429
		<m:pre jazyk="bash"><![CDATA[curl \
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   430
	--header "Accept: text/csv" \
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
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parents:
diff changeset
   431
	--data-urlencode query="SELECT * WHERE { ?subject ?predicate ?object . } LIMIT 3" \
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
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parents:
diff changeset
   432
	https://dbpedia.org/sparql | relpipe-in-csv | relpipe-out-tabular]]></m:pre>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
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parents:
diff changeset
   433
	
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   434
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   435
			It becomes bit longer if we add some documentation, argument parsing and configuration:
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   436
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   437
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
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parents:
diff changeset
   438
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   439
		<m:pre jazyk="bash" src="examples/relpipe-in-sparql.sh" odkaz="ano"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   440
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   441
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   442
			Here we have even two implementations that could be switched using the <code>RELPIPE_IN_SPARQL_IMPLEMENTATION</code> environmental variable.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   443
			The XML one is more powerful and can be customized (e.g. to specifically handle localized strings or add some new attributes to the relational output).
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   444
			On the other hand, the CSV one has fewer dependencies and support streaming of long result sets (XSLT needs to load whole document first).
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   445
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   446
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   447
		<p>Both implementation should work:</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   448
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   449
		<m:pre jazyk="bash"><![CDATA[export RELPIPE_IN_SPARQL_IMPLEMENTATION=xml
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   450
export RELPIPE_IN_SPARQL_IMPLEMENTATION=csv
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František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   451
echo 'SELECT * WHERE { ?subject ?predicate "Laura Dern"@en . } LIMIT 3' \
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   452
	| relpipe-in-sparql \
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   453
		--relation "jurassic" \
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   454
		--endpoint "https://dbpedia.org/sparql" \
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   455
	| relpipe-out-tabular]]></m:pre>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
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parents:
diff changeset
   456
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   457
		<p>and produce the same output:</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   458
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   459
		<pre><![CDATA[jurassic:
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   460
 ╭────────────────────────────────────────┬────────────────────────────────────────────╮
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   461
 │ subject                       (string) │ predicate                         (string) │
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   462
 ├────────────────────────────────────────┼────────────────────────────────────────────┤
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   463
 │ http://dbpedia.org/resource/Laura_Dern │ http://www.w3.org/2000/01/rdf-schema#label │
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   464
 │ http://www.wikidata.org/entity/Q220901 │ http://www.w3.org/2000/01/rdf-schema#label │
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   465
 │ http://dbpedia.org/resource/Laura_Dern │ http://xmlns.com/foaf/0.1/name             │
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   466
 ╰────────────────────────────────────────┴────────────────────────────────────────────╯
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
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parents:
diff changeset
   467
Record count: 3]]></pre>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   468
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   469
		<p>And maybe somewhere nearby in the graph we will find:</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   470
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   471
		<blockquote>It's a Unix System… I know this!</blockquote>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   472
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   473
		<h2>Sources of RDF data</h2>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
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parents:
diff changeset
   474
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   475
		<p></p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   476
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   477
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   478
			The bad news are that we are not querying the real world. 
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   479
			We are querying an imperfect, incomplete and outdated snapshot of the reality stored in someone's database.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   480
			The good news are that we can improve the content of certain databases like we improve articles in Wikipedia.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   481
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   482
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   483
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   484
			Some addresses have already <i>leaked</i> in the <code>relpipe-in-sparql --help</code> above.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   485
			Here is brief description of some publicly available sources of RDF data
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   486
			that we can play with.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   487
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   488
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   489
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   490
		<h3>Wikidata</h3>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   491
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   492
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   493
			A free and open knowledge base, a sister project of Wikipedia.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   494
			Anyone can use and even edit its content.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   495
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   496
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   497
		<m:sparql-endpoint url="https://query.wikidata.org/sparql" website-url="https://www.wikidata.org/" website-title="Wikidata"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   498
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   499
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   500
		<h3>DBpedia</h3>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   501
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   502
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   503
			They extract structured content from the information created in various Wikimedia projects.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   504
			And publish this knowledge graph for everyone.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   505
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   506
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   507
		<m:sparql-endpoint url="https://dbpedia.org/sparql" website-url="https://wiki.dbpedia.org/" website-title="DBpedia"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   508
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   509
		<h3>Czech government</h3>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   510
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   511
			Ministries and other institutions publish some data as open data and part of them as linked open data (LOD).
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   512
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   513
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   514
		<m:sparql-endpoint url="https://data.gov.cz/sparql" website-url="https://data.gov.cz/english/" website-title="Open data portal of the Czech Republic"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   515
		<m:sparql-endpoint url="https://data.cssz.cz/sparql" website-url="https://data.cssz.cz/" website-title="Open data portal of the Czech Social Security Administration"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   516
		<m:sparql-endpoint url="https://cedropendata.mfcr.cz/c3lod/cedr/sparql" website-url="https://cedropendata.mfcr.cz/" website-title="Open Data CEDR III"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   517
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   518
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   519
		<h2>Running SPARQL queries as scripts</h2>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   520
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   521
		<p>Besides piping SPARQL queries through <code>relpipe-in-sparql</code> like this:</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   522
		<m:pre jazyk="bash"><![CDATA[cat query.sparql | relpipe-in-sparql | relpipe-out-tabular]]></m:pre>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   523
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   524
		<p>we can make them executable and run like a (Bash, Perl, PHP etc.) script:</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   525
		<m:pre jazyk="bash"><![CDATA[chmod +x query.sparql
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   526
./query.sparql | relpipe-out-csv     # output in the CSV format
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   527
./query.sparql | relpipe-out-recfile # output in the Recfile format
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   528
./query.sparql                       # automatically appends relpipe-out-tabular to the pipeline
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   529
]]></m:pre>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   530
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   531
		<p>(see the <m:a href="implementation">Implementation</m:a> page for complete list of available transformations and output filters)</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   532
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   533
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   534
			We need to add the first line comment that points to the interpreter.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   535
			The <code>endpoint</code> and <code>relation</code> parameters
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   536
			are optional – we can say, where this query will be executed and how the output relation will be named:
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   537
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   538
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   539
		<m:pre jazyk="sparql" src="examples/rdf-sample-triples.sparql" odkaz="ano"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   540
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   541
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   542
			Environmental variables <code>RELPIPE_IN_SPARQL_ENDPOINT</code> and <code>RELPIPE_IN_SPARQL_RELATION</code>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   543
			can be set to override the parameters from the file.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   544
			All the magic is done by this (bit hackish) helper script:
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   545
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   546
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   547
		<m:pre jazyk="bash" src="examples/rdf-sparql-interpreter.sh" odkaz="ano"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   548
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   549
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   550
			This script requires the <code>relpipe-in-sparql</code> we put together earlier.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   551
			Both scripts are just examples (not part of any release yet).
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   552
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   553
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   554
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   555
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   556
		<h2>Samples of SPARQL queries</h2>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   557
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   558
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   559
			<i>Hey kid, rock and roll,</i>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   560
			let us list the films where both Coreys starred:
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   561
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   562
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   563
		<m:sparql-example name="examples/rdf-coreys"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   564
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   565
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   566
			<i>So Mercedes has scratched our Cadillac, but it was still a great night. </i>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   567
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   568
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   569
		<p>Now it is time to visit our friends from the club:</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   570
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   571
		<m:sparql-example name="examples/rdf-breakfast-club"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   572
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   573
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   574
			Not only <i>pretty in pink</i>, this is true <i>wisdom</i> and we could have much fun traversing this part of the graph.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   575
			But let us turn the globe around… there is also a lot to see in the Eastern Bloc.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   576
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   577
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   578
		<m:sparql-example name="examples/rdf-blonde-and-brunette"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
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diff changeset
   579
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   580
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   581
			<i>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   582
				Dad, what is this place?
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   583
				Where are we?
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   584
				Is there anyone here?<br/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   585
				No. Just us.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   586
			</i>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   587
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   588
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   589
		<m:sparql-example name="examples/rdf-return"/>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   590
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   591
		<h2>P.S.</h2>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   592
		<p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   593
			<i>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   594
				If you got an impression that RDF is just a poor relational database with a single table consisting of mere three columns
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   595
				and with freaky SQL dialect, please be assured that this example shows just a small fraction of the wonderful RDF world.
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   596
			</i>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   597
		</p>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   598
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   599
		
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   600
	</text>
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   601
aeda3cb4528d examples: Querying an RDF triplestore using SPARQL
František Kučera <franta-hg@frantovo.cz>
parents:
diff changeset
   602
</stránka>