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Re: Objects and Relations

From: Marshall <>
Date: 1 Feb 2007 10:46:13 -0800
Message-ID: <>

On Feb 1, 12:37 am, "David BL" <> wrote:
> On Feb 1, 4:04 pm, "Marshall" <> wrote:
> > Um, but isn't the number of different possible, joins say, a
> > function of the number of attributes? So we shouldn't be
> > surprised that relations with fewer attributes have fewer
> > possible joins.
> Yes. However it seems to me that the fact that you're willing to use
> nested relations for strings reveals that you don't expect a string
> relation to join usefully with the other relations. Does that
> willingness to isolate the relation indicate something?

Uh, I would disagree with the word "isolate." If anything, wanting to treat strings as relations is a endorsement of the use of the RA. Current DBMSs treat strings as something non-relational; a special purpose attribute type. My feeling is that we should treat everything as relations as can be, including attributes (where appropriate,) and including lists

> In my OP for this thread I distinguished between entities that are
> part of the abstract computational machine, and external entities.
> Do you agree that the distinction is well defined? Note that one of
> the "fights" on comp.object was over this question.

I agree it's a clear distinction ...

> If the distinction is meaningful, then it seems to follow that you
> wouldn't want to mix facts about internal entities and facts about
> external entities at the one level of abstraction.

I suppose so, but I think what this is saying is that we need logical/physical separation. If you have a language in which you don't have that, you have no choice but to mix.

> Is it possible that your willingness to use a nested relation exactly
> correlates with the distinction between internal and external
> entities?

I see no reason to think so.

> At the very least I find this to be an interesting
> conjecture. It makes strong predictions about relational designs.
> The conjecture that OO should keep away from storing information about
> external entities is also powerful. It puts the OO animal in a nice
> little cage.

I have some sympathy with your position, but it appears impractical to someone who is currently writing software in an OOPL.

> It seems a little peculiar to me to store facts about entities that
> are in fact part of the abstract computational machine. Why would a
> machine store facts about its own working parts? To me a machine just
> "is". Now I guess this is a rather weak argument because a machine
> may be based on logic or set theory. In any case it is an interesting
> conjecture just in case RM indeed proves to be deficient for
> constructing computational machines. Curiously RM would be ideal for
> storing facts about a given computational machine.

I figure one wants reflection and you want a "system catalog."

Marshall Received on Thu Feb 01 2007 - 12:46:13 CST

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