For example, given three nodes, e1, e2, and e3, a local method can possibly classify (e1,e2)=before, (e2,e3)=before, and (e1,e3)=after, which is obviously wrong since before is a transitive relation and (e1,e2)=before and (e2,e3)=before dictate that (e1,e3)=before.
time is an important dimension of knowledge representation.