Rational is the head used for rational numbers.

Graph[{e1, e2, ...}] yields a graph with edges ej. Graph[{v1, v2, ...}, {e1, e2, ...}] yields the graph with vertices vi and edges ej. Graph[{..., wi[vi, ...], ...}, {..., wj[ej, ...], ...}] yields a graph with vertex and edge properties defined by the symbolic wrappers wk. Graph[data] yields a graph from data.