In the case where a relationship has a relationship, we can use aggregation. An example could be a relationship between consultants working on projects, where one consultant works on at least one project (1..n) and one project can have zero to many consultants working on it (0..n).
Then apart from this relationship, there is a relationship between these project participations and a contract, where one contract has at least one consultant participating in a project that it relates to.
For the depiction in a diagram, see ER diagram.
