Circular references
From Robs_Wiki
Explanation 1: A circular reference is a series of references where the last object references the first, resulting in a closed loop.
Explanation 2: A circular relationship exists when every occurrence of entity A has one or more occurrences of entity B; entity B has one or more occurrences of entity C; and entity C has one or more
occurrences of entity A
A => B => C => A
You can prevent circular references by using a link table:
A => ABC B => ABC C => ABC