I have this ER diagram, which supposedly has two cycle relationships. I have doubts because one person says that it is indeed cycle relationships, and another person says that it does not. The diagram can be found at: http://www.jmontalvo.com/registrations1000x900.jpg.
You diagram is really hard to read on a 160 by 160 display, but the only circular reference I can see (where an entity contains its own Primary Key as a Foreign Key too) is AppUser. You could create a true circular reference there.
A cycle relationship is more complex, where some group of entities refer to each other in such a way that it is possible to create a "loop" of relationships that feed back into itself. There are several possible 1:N relationships that could generate a cycle, but I can't see how they would naturally assume a cycle.
The short answer is yes, a cycle is possible in more than one way, but I don't see how it would occur naturally.
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