RDF data management and processing

This session will be about managing RDF data programmatically. We will set up an RDF data base (also called a triplestore). We will convert existing, non-RDF data, into RDF, programmatically, then load it to the triplestore.

Generate RDF with Apache Jena

These instructions assume that you are programming in Java, preferably with Eclipse, using the Apache Jena libraries. You may also use RDF4J in Java, RDFlib in Python, or Redland RDF libary in C, or dotNetRDF in C♯, or EasyRDF for PHP, or N3.js for JavaScript, or Ruby RDF for Ruby, or SWI-Prolog Semantic Web Library, etc.

These operations should get you started with Apacha Jena and Eclipse. With a different IDE for Java, the only difference will be the initial settings for a Mavan project. If you are using a different library, look at the documentation.

Now you will generate RDF data from non-RDF sources. Read the Jena tutorial to familiarise yourself with the API and learn how to generate an RDF graph programmatically. Once you are done with the tutorial, follow the instructions below.

Setting up a triplestore

There are many triplestores. The simplest to set up is probably Fuseki.

In the exercise of the first part, you can generate all the data at once in a large Jena Model and serialise it as RDF, or you can fill in a triplestore little by little. If you want to add data to a triplestore such as Jena Fuseki, you can send update queries like this:

Model model = ModelFactory.createDefaultModel();
// ... build the model
String datasetURL = "http://localhost:3030/sncf";
String sparqlEndpoint = datasetURL + "/sparql";
String sparqlUpdate = datasetURL + "/update";
String graphStore = datasetURL + "/data";
RDFConnection conn = RDFConnectionFactory.connect(sparqlEndpoint,sparqlUpdate,graphStore);
conn.load(model); // add the content of model to the triplestore
conn.update("INSERT DATA { <test> a <TestClass> }"); // add the triple to the triplestore

Interacting with a remote SPARQL endpoint

In this part, you will link your new dataset to Wikidata. To do that, you will query the SPARQL endpoint of Wikidata in your program. In Jena, you can send queries like this:

String wdEndpoint = "https://query.wikidata.org/sparql";
RDFConnection wdConn = RDFConnectionFactory.connect(wdEndpoint);
QueryExecution qe = wdConn.query("SELECT ?s WHERE { ?s a <TestClass> }");
ResultSet res = qe.execSelect();

Refer to the Jena tutorial on RDF connections for more details.

As before, you can use store the collected information in a Jena Model (and then, serialize it in Turtle) or insert it little by little in a local triplestore.

Interacting with a Linked Data Platform

To interact programmatically with a Linked Data Platform (as in practical session 3), you need to rely on an HTTP library in your programming language. You may use the Apache HTTP Client in Java (which is also a Jena dependency), or URLlib in Python, etc. Instead of using cURL, you can send POST requests with appropriate Turtle payloads via the programming interfaces.

Write a program that reproduces the steps of practical session 3 (Publishing data on a Linked Data Platform).