A recursive relationship is a rule that exists between instances of the same entity. A one-to-many recursive relationship describes a hierarchy, whereas a many-to-many relationship describes a network. In a hierarchy, an entity instance has at most one parent. In a network, an entity instance can have more than one parent.
Let’s illustrate both types of recursive relationships using Employee. See Figure 7.5 for a one-to-many recursive example and Figure 7.6 for a many-to-many example.
Figure 7.5 An Employee may work for one Manager
· Each Employee may manage one or many Employees.
· Each Employee may be managed by one ...