Re: Searching OO Associations with RDBMS Persistence Models

From: Robert Martin <>
Date: Fri, 16 Jun 2006 08:42:01 -0400
Message-ID: <2006061608420175249-unclebob_at_objectmentorcom>

On 2006-06-06 06:29:31 -0400, "Cimode" <> said:

> I do not quite understand the following sentencesR Martin used...
> "They were semantic elements that had identity"
> then..
> "but they weren't database entities, and so the concept of "key" was
> superfluous"
> How did you define *identity* on these semantic elements without a key?
> What other mechanism of identification have you used to coherently
> identify these semantic elements? Do you suppose they is a need to
> distinguish them or not?
> Just curious.

An object has an intrinsic identity within the computer. You could think of this identity as the pointer to the object; but this is an approximation at best. Some languages expose the numeric value of that pointer, and some don't. Others allow an object to have more than one address. So, although an object is a tuple, the notion of a key as one of the fields of the tuple that uniquely identifies the tuple, is not part of OO.

Robert C. Martin (Uncle Bob)  | email:
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Received on Fri Jun 16 2006 - 14:42:01 CEST

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