History

• Originally called Titan. It was renamed to JanusGraph in 2015.

Data Model

Query Interface[04]

JanusGraph uses Gremlin graph query language to retrieve data from and modify data in the graph. Gremlin is a functional language whereby traversal operators are chained together to form path-like expressions, expressing query or data modification on graphs.

A Gremlin query is a chain of operations/functions that are evaluated from left to right. A simple example of gremlin language to query the name of Alex's grandson on his genealogy graph is provided below

g.V().has('name', 'Alex').out('father').out('father').values('name')

The query can be read as
g : for the current graph
V : for the vertices in the graph
has('name', 'Alex') : filters the vertices down to those with the "name" property "Alex"
out('father') : traverse outgoing through edges whose type is "father" from "Alex" (Notice here the result can be more than one vertices)
out('father') : traverse outgoing through edges whose type is "father" from "Alex"' son (the result from the last traversal)
values('name') : get the property of "name"

Other more complex examples of Gremlin can be found in
Complete Gremlin Manual

There're two ways to query JanusGraph with Gremlin

• First one is to use Gremlin Console, Gremlin Console is an interactive shell that is distributed with JanusGraph, by connecting Gremlin Console to JanusGraph Server, users can directly interact with graphs stored in JanusGraph Server using Gremlin.

• The second one is to embed Gremlin code into your Java Application using JanusGraph Java API as shown below

Traversal t = g.V().has("name", "pluto"); // Define a traversal. // Note the traversal is not executed/iterated yet Vertex pluto = null;
if (t.hasNext()) { // Check if results are available
pluto = g.V().has("name", "pluto").next(); // Get one result
g.V(pluto).drop().iterate(); // Execute a traversal to drop pluto from graph
}
// Note the traversal can be cloned for reuse
Traversal tt = t.asAdmin().clone();
if (tt.hasNext()) {
System.err.println("pluto was not dropped!");
}
List gods = g.V().hasLabel("god").toList(); // Find all the gods