Bipartite Graphs

This problem is naturally expressed as a bipartite graph.

Such a graph G=(V,E) has a set of nodes L and a set of nodes R such that $L \cap R = \emptyset$, $L \cup R = V$ (partition: mutually exclusive and exhaustive), and for all $(u,v)\in E$, $u \in L$ and $v \in R$.

Also natural for machines-tasks, classes-classrooms, and others?