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Re: Extending my question. Was: The relational model and relational

From: Bernard Peek <bap_at_shrdlu.com>
Date: Tue, 18 Feb 2003 23:16:11 +0000
Message-ID: <oU8bYjG76rU+EwVd@diamond9.demon.co.uk>


In message <b2uat1$f0t$1_at_slb9.atl.mindspring.net>, Steve Kass <skass_at_drew.edu> writes

>Bernard,
>
> This isn't a matter of opinion. There is one determinant: "there are two
>employees named John Smith". There are many consequential
>truths, such as "there is at least one employee", "there is an employee
>whose first name is not Nancy", "there are at least two employees
>whose first and last names share a common letter of the alphabet.",
>and so on.
>
> I don't deny that it can be important to distinguish between two
>John Smiths.

That's not my argument. My argument is that there may be no need to distinguish between two real-world objects, each of which is referenced by a single record in a database. The relational model (and databases based on it) require that a distinguishing key be created even if there is none in the logical data structure.

I don't dispute that there are real pragmatic reasons for accepting that deviation from the logical structure of the data. But as this is a theory newsgroup I wanted to point out that this is a (minor) failing in the relational model.

[...]

> I'm not redefining any words, but we have a fundamental
>difference in understanding logical vs. physical models. You are
>saying that the real-world scenario of books in a library must be
>represented by a logical model that does not keep track of an
>actual attribute of "book" (acquisition number), and then you
>blame the model for not being able to distinguish two identical
>books,

No, that's not my objection. My objection is that the relational model declares that there must be a distinction, when there is no such requirement in the real world.

It does makes the maths easier, and it makes the implementation much easier.

-- 
Bernard Peek
bap_at_shrdlu.com
www.diversebooks.com: SF & Computing book reviews and more.....

In search of cognoscenti
Received on Tue Feb 18 2003 - 17:16:11 CST

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