The IBM Graph DB service is one of the many data and analytics services available on Bluemix. If you are not familiar with graph databases, than you can read more about them on Wikipedia. The primary use case for graph databases is to describe relationships between different objects. Graph DBs are composed of two components, vertices and edges. A vertex represents some type of object and an edge represents a relationship between two vertices. The classic example is to represent your social network via a graph database. Each vertex represents a person and an edge between a person represents the fact that those two people know each other. Vertices and edges can have properties associated with them. For example, a person might have a name property associated with the vertex. An edge between two people might have a property representing the date the relationship was established.