a graph is just a collection of vertices and edges—or, in less intimidating lan‐
guage, a set of nodes and the relationships that connect them. Graphs represent entities
as nodes and the ways in which those entities relate to the world as relationships. This
general-purpose, expressive structure allows us to model all kinds of scenarios, from
the construction of a space rocket, to a system of roads, and from the supply-chain or
provenance of foodstuff, to medical history for populations, and beyond.