Re: General semantics

From: Clifford Heath <>
Date: Sat, 22 May 2010 20:44:46 +1000
Message-ID: <4bf7b59e$0$3516$>

Nilone wrote:
> ...However, I see it as one of the
> weaknesses of OOP that I can't query the set of all instances of a
> class.

The weakness is caused by OOP's use of extrinsic identification. It's a serious problem, in fact it's the antithesis of what makes the RM special. See my other post on this subject.

> I could use a static private List or Dictionary to keep track
> of instances, but that would interfere with the GC reclaiming the
> object automatically.

Not if you use a weak reference, assuming your GC supports that. Java does, for example.

> Please don't ask me to map from the relational model to OOP. I can't
> do so in general, since the RM has greater expressive power than OOP.

I don't think you can make a statement like that. There is no definitive formal model of what OOP is, so you cannot say what it is or is not capable of. It is true however that there could exist OOP implementations of RM, at least in theory, so one must assume it has at least equivalent power.

That's not a recommendation of OOP, just a request to be careful with your claims. Received on Sat May 22 2010 - 12:44:46 CEST

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