So far, we've only talked about graphs as a set of connected nodes. Those connections can be different depending on whether you are going from node A to node B or vice versa. For instance, some streets can only be driven in one direction, right? Or, the fact that you are following someone on Twitter (there is a Follows relationship from you to that user) doesn’t mean that user is also following you. That’s the reason why some relationships are directed. On the contrary, a relationship of type married to is naturally undirected, if A is married to B, usually B is also married to A:
In the right-hand side graph, directed, the transition between B and A is not allowed in that direction
In Neo4j, all relationships are directed. However, Cypher allows you to take this direction into account, or not. That will be explained in more detail in Chapter 2, The Cypher Query Language.
