(mix, max) notation for relationships

Structural constraints are specified on each participation of an entity type E in a relationship type R. It specifies that each entity e in E participates in at least min and at most max relationship instances in R.

• By default, with no constraint, min = 0 and max = n (no limit).
• Must have min $\le$ max, min $\ge 0$, and $max\ge 1$.
• Derived from knowledge of mini-world constraints.