A Property Graph has a set of Vertices and a set of Edges.
Each Vertex has:
- A unique Identifier.
- A set of outgoing Edges.
- A set of incoming Edges.
- A collection of properties defined by a map from key to value.
Each Edge has:
- A unique Identifier.
- An outgoing tail vertex.
- An incoming head vertex.
- A label that denotes the type of relationship between its two vertices.
- A collection of properties defined by a map from key to value.
