Re: Mixing OO and DB

From: Robert Martin <>
Date: Sun, 24 Feb 2008 09:35:44 -0600
Message-ID: <2008022409354475249-unclebob_at_objectmentorcom>

On 2008-02-22 13:54:40 -0600, Marshall <> said:

> A model of a circle is a circle is an ellipse.

I think this is a 2500 year old argument that you and I are not going to resolve. Suffice it to say that I disagree. To me (2,2,3) *represents* a circle, but is not in and of itself a circle.

> An instance of a mutable circle class is not an instance
> of a mutable ellipse class. That's where the problem
> lies.

Mutability is one kind or property that is not substitutable accross circle/ellipse relationship. I'm sure we could find others. I agree that if you exclude all the unsubstitutable properties, you can make class circle a subtype of class ellipse. On the other hand, if you exclude all the unsubstitutable properties you can make any type S a subtype for any type T.

Robert C. Martin (Uncle Bob)  | email:
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Received on Sun Feb 24 2008 - 16:35:44 CET

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