You can do this, but it is not a built in primitive (like it is in Neo4j). We chose to do this because the majority of edges are usually directed, and we wanted to keep the base system as small as possible (all of gun is only about 12KB). It is easy to create "edge" nodes that store relationship properties, but nobody has created a full feature extension/framework for this yet, but I expect one will be built because this is a very useful feature to have.