"Structured" Entity-Relationship Model?

coming from the "practitioner" side, I wonder what relational theorists think about "structured entity relationship" modelling:

http://en.wikipedia.org/wiki/Structured-Entity-Relationship-Model

For me the essential aspect seems to be the rule (which doesn't even seem to be mentioned in the english-language Wikipedia article) that the dependency graph of all entities must not contain directed circles, i.e. there must be no "hen and egg"-type dependencies between entities.

Which appears to be a perfectly reasonable rule to me, since such dependencies create horrible headaches for working with such databases. Just imagine loading or deleting bulk data with circular dependencies.

Now what do theorists think:

Is it perfectly evident that this requirement must be enforced, since a model with cyclic dependencies is plain "spaghetti", maybe even violating some normal form? Is it plain nonsense? Or does it depend on the specific case, since there may be situations where it can't be achieved, and a model that violates this rule can be perfectly valid?

I've noted that in practice, graphical modelling tools seem to be prone to making users produce models where this rule is violated. There don't seem to be modeling tools that would allow checking for such dependencies resp. preventing them.

TIA, Sincerely,

Wolfgang Received on Sat Apr 20 2013 - 22:02:46 CEST