Re: circular relationships ok?
Date: Thu, 02 Mar 2006 18:07:47 +0100
David Portas schrieb:
> Alexandr Savinov wrote:
>> Customer Product >> \ / >> Favorite(c,p) >> >> Now we can get a list of favorite products for a customer and a list of >> customer for this product as a favorite. >>
> But now you've removed Order from and Item from the diagram. Are you
> saying you can only avoid loops by drawing 2 diagrams instead of 1?
I simply cannot draw it. There exist only one diagram and it describes one model:
Top / \ Customer Product | \ / | | \/ | | /\ | Order / \ | | / Favorite Item / \ / Bottom
(Top and Bottom are useful in theory as the most abstract and the most specific concepts.)
>> I do not see in your SQL example circular references.
> Then you didn't draw the ER diagram for the constraints in that schema.
Then explain please what you mean.
>>> Can "concept oriented" enforce such constraints? >>> If so, how do you draw diagrams of them without loops? >> A model with cycles is not a concept-oriented model (theoretically). It >> is a strong constraint but it is part of the definition. Then the >> question is if it is useful or not.
> I think that means No. You are saying I have to change my business
> rules for concept-oriented to work?
What if your business rule says that we need to use goto in programming? I just want to say that concept-oriented approach is able to describe a wide spectrum of real world models. Give me an example and I will try to model it.Received on Thu Mar 02 2006 - 18:07:47 CET