title: When to use ternary relationship instead of aggregation in RDBMS?
body: <p>I was wondering when one would represent a relationship between an entity set and a relationship with a ternary relationship?  I understand the benefit of aggregation, but why use it if there is no attribute in the relationship between the entity set and the relationship set? For instance, a grad student (with a student # and name) works on a project (with pid, start date, and end date) and each project that a student works on has a supervising professor. Every project must have only one professor as supervisor.  The supervisor relation has no attribute that is unique yet I have been told that aggregation should be used, but why?</p>