I made use of colors to get around this problem. We can render related events with similar colors. Events that don't participate in any relationship continue to have their default color. This way we can avoid use of lines altogether.
When drawing relationships, type of relationship needs to be considered. In particular, we need to ask the question, "Are the relatrionships transitive?". For example, if Mozart's work is influenced by Bach and Beethovan's work is influenced by Mozart. Then, is Beethovan's work, influenced by Bach?. If yes, then we can render all three composers by the same color. However, if transitivity does not hold, then how would you represent Bach and Mozart woth one color and Mozart and Beethovan with a completely different color ?
We need to think of a new way to display non-transitive relationships ..
Notice that this wasn't a problem, had we stuck to arrow headed lines.