I read the following on the wikipedia article on binary relations:
A binary relation R between arbitrary sets (or classes) X (the set of departure) and Y (the set of destination or codomain) is specified by its graph G, which is a subset of the Cartesian product X × Y.
Is it really necessary to define relations in terms of graphs? Why do we need to introduce this aditional concept at this point? It seems to me that graphs are distinct mathematical objects with a lot more baggage than a mere subset which may be all we need at this point. What's wrong with simply saying:
A binary relation R between arbitrary sets (or classes) X (the set of departure) and Y (the set of destination or codomain) is a subset of the Cartesian product X × Y.