Using Tinkerpop

Using OGIT with Apache Tinkerpop

Apache Tinkerpop is the De-facto standard abstraction for graph databases in Java. It comes with the Gremlin query language. The most important parts of Tinkerpop are the API and the Gremlin language, but the Apache project also provides a server implementation and a console (REPL). The following steps help you to get started with OGIT in Tinkerpop using a simple in-memory graph, but for a production system, you might want to have a look at the Tinkerpop-compatible providers. Here we will start the interactive, Groovy-based Gremlin shell, load OGIT into it and run a query. Note that for Tinkerpop 2.x, there exists an adapter to OpenRDF’s SAIL interface, which allows the graph database to be accessed like a triple store. In this tutorial we will use Tinkerpop 3.x, which has an API that is incompatible with Tinkerpop 2.x. It’s still easy to import the RDF though, as you will see below.

1. We will use the rapper command-line utility to merge all of OGIT’s turtle files into one file in N-Triples-Format. In a Debian-based system, you can install it by running apt-get install raptor2-utils. Clone the OGIT repository, then in the OGIT directory run:

   rapper -i turtle -o ntriples <(find . -name '*.ttl' -exec cat "{}" \;) > ogit.nt

2. Download and extract the Apache Gremlin Console.

3. From the extracted directory, run:

   bin/gremlin.sh

   This opens the the Gremlin REPL.

4. Move or link the ogit.nt to the directory of the Gremlin console. Save the following script in the same directory as ogit.gr. This Groovy script can be loaded by Gremlin and will insert OGIT's RDF statements into an in-memory graph store. This is fine for testing purposes, for large use cases you should consult Gremlin’s documentation.

   graph = TinkerGraph.open()
   g = graph.traversal()
   
   node = { id ->
   	g.V().has(T.label, id).tryNext().orElseGet{ g.addV(T.label, id).next() }
   }
   
   new File('ogit.nt').eachLine {
   	(s, p, o) = it.replaceAll(" \\.\$", "").split(" ", 3).collect { i -> i.substring(1, i.length() - 1) }
   	node(p)
   	if (!o.isEmpty()) {
   		node(s).addEdge(p, node(o))
   	}
   }

5. In the Gremlin console, type:

   :load ogit.gr

6. Now we can query the graph. Enter the following query. This will list the names of the Entities defined in OGIT.

   g.V().has(T.label, "http://www.purl.org/ogit/Entity").in("http://www.w3.org/2000/01/rdf-schema#subClassOf").label()