Re: circular relationships ok?

From: Alexandr Savinov <>
Date: Thu, 02 Mar 2006 18:07:47 +0100
Message-ID: <44072663$>

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:

        /   \
  Customer  Product
      |   \  / |
      |    \/  |
      |    /\  |
    Order /  \ |
      |  / Favorite
     Item    /
       \    /

(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

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