out() vs. outE() — JanusGraph and Gremlin

If you are new to JanusGraph and the Gremlin query language, like I am, you would be confused about the out(), outE(), in(), and inE() methods. If you look at examples of these functions, you'll not be able to comprehend the difference easily. Or is it just me?

Anyway, I got confused and it took me a while to understand there is a difference, and there isn’t. Let me explain.

The Sample Graph

Before we look at the differences, let’s look at a sample graph.

As you can see from the graph above, we have four vertices and three edges. The vertex in the middle with the property "name": "sunny" is the vertex from where we'll start our traversal. The other three vertices are the items that I bought from an e-commerce website. They are a smartphone, a laptop, and a monitor. The relationship is represented with edges labelled bought.

The edges have another property called count, and as you can tell, they represent the number of times I have bought these items. So I bought three smartphones, two laptops, and one monitor. This is the data we're going to work with.

Now, we’ll first get a reference to our starting vertex with the following query:

sunny = g.V().has('name', 'sunny').next()