[russian] Как гарантировать наличие атрибута (циклическая зависимость) / Проектирование БД : Форум на SQL.RU | about cyclic references / database design
good discussion about cyclic references. Basically the main point is that if you have a question "how do I implement cyclic fererence?" -- then there is something wrong, 99% that it is so because ur understaning of problem domain is wrong.