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Re: Searching OO Associations with RDBMS Persistence Models

From: Keith H Duggar <duggar_at_alum.mit.edu>
Date: 19 Jun 2006 19:33:38 -0700
Message-ID: <1150770818.309746.45280@b68g2000cwa.googlegroups.com>


Robert Martin wrote:
> Cimode wrote:
> > 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.

Aren't /this/ in C++ and /self/ in SmallTalk conceptually fields? (Albeit second-class fields.) And the fact that in C++ an object can have multiple numerical addresses is just an implementation artifact. Suppose this were not the case. In other words, suppose a hypothetical language in which every object had a unique numerical address. Would that still be an approximation of indentity? If so why?

Do you find any of the arguments in favor of representing identity as explicit data reasonable? If so which ones? Finally, which argument(s) against explicit representation of identity do you find most compelling?

Received on Mon Jun 19 2006 - 21:33:38 CDT

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