Laying the Foundation of a Semantic Web Application : Page 2

Loading Data Into Jena SDB
The example RDF model from the previous article Why Migrate to the Semantic Web can be loaded in SDB using the command:

SDBROOT > bin/sdbload --sdb=sdb.ttl http://www.3kbo.com/examples/building.rdf

The SDB Commands provide a number of ways to check whether the data loaded correctly.

A generic test is to run the sdbdump command, which lists all the RDF triples loaded:

SDBROOT > bin/sdbdump --sdb=sdb.ttl

Use the sdbquery command to make SPARQL queries. For example, the following lists the RDF triples in simple table form:

SDBROOT > bin/sdbquery --sdb=sdb.ttl 'SELECT ?s ?p ?o WHERE {?s ?p ?o }'

This command writes out the model in N3 format:

SDBROOT > bin/sdbquery --sdb=sdb.ttl 'CONSTRUCT {?s ?p ?o} WHERE {?s ?p ?o }'

You can list all people in the model with the query:

SDBROOT > bin/sdbquery --sdb=sdb.ttl 'CONSTRUCT {?s ?p ?o} WHERE {?s ?p ?o .  ?s a 
<http://xmlns.com/foaf/0.1/Person>}'

Details of the BreakerBay building project are provided with the query:

SDBROOT > bin/sdbquery --sdb=sdb.ttl 'CONSTRUCT {<http://3kbo.com/examples/building.rdf#BreakerBay> ?p ?o}
 
WHERE {<http://3kbo.com/examples/building.rdf#BreakerBay> ?p ?o }'

This gives the result:

:BreakerBay
      rdf:type      :BuildingProject ;
      rdfs:comment  "House extension and landscaping" ;
      rdfs:label    "Breaker Bay "^^xsd:string ;
      :approvedBy   :WellingtonCityCouncil ;
      :builtBy      :GarethEvans ;
      :designedBy   :AlexGreig ;
      foaf:based_near <http://dbpedia.org/resource/Wellington> ;
      foaf:fundedBy  :RichardHancock .

Creating a Maven-based Web Application
Use Maven to manage the dependencies between the various component libraries required by the application. Download and install it from the Maven site if it is not installed already.

Running the following maven command creates the initial project structure of a maven based web app application, creating a top level directory named "sdb-joseki".

mvn archetype:create -DgroupId=com.devx -DartifactId=sdb-joseki -DarchetypeArtifactId=maven-archetype-webapp

Author's Note: If you are new to Maven check out the instructions for Building a Project with Maven.

Download and unzip Joseki and copy the contents of the Joseki-3.2/webapps/joseki directory to the sdb-joseki/src/main/webapp directory as shown in Figure 1.

Figure 1. Project Structure: Copy the contents of the directory.

From the source code, add the provided joseki-config.ttl and log4j.xml files to the src/main/resources directory and replace the generated pom.xml with the one provided.

The joseki-config.ttl file configures Joseki to work with the RDF data loaded into SDB. (Change the username and password in the joseki-config.ttl file to match that used for the MySQL "sdb" database.)

In the WEB-INF/web.xml file, comment out the servlet-mapping for books url-pattern because only the default graph was configured in joseki-config.ttl file.

<!-- Demo service 
  <servlet-mapping>
    <servlet-name>SPARQL service processor</servlet-name>
    <url-pattern>/books</url-pattern>
  </servlet-mapping>
  -->

The provided pom.xml file contains all the dependencies needed to build the sdb-joseki.war file, however joseki.jar is not available from an external maven repository.

On the command line, change into the directory Joseki-3.2/lib and add joseki.jar to the local maven repository by running the command:

mvn install:install-file -DgroupId=org.joseki -DartifactId=joseki -Dversion=3.2 -Dpackaging=jar -Dfile=joseki.jar

Change into the directory sdb-joseki. The sdb-joseki.war file can now be built by running the command:

mvn package 

Deploy the sdb-joseki.war file to Tomcat to provide a SPARQL endpoint querying the default graph, i.e., the data loaded into SDB. Test that the SPARQL endpoint is working by opening the form at http://localhost:8080/sdb-joseki/sparql.html and submitting the query 'CONSTRUCT {?s ?p ?o} WHERE {?s ?p ?o }'.

In Firefox, with the Tabulator Extension installed, the default graph is displayed as per Figure 2. Another query to try is " CONSTRUCT {?s ?p ?o} WHERE {?s ?p ?o . ?s a <http://xmlns.com/foaf/0.1/Person>}", which results in Figure 3.

Figure 2. Default Graph: How the default graph appears with the Tabulater Extension installed.

Figure 3. Listing Of People: A certain query provides a listing of people.

At this point, you have laid the foundation of a semantic web application and you have created a maven web application project that implements an RDB triple store using Jena SDB and a SPARQL endpoint via Joseki. The next article in this series will discuss adding the Spring Security and JAX-RS to enable the publication of public and private Linked Data.

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