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

From: Bernard Peek <>
Date: Tue, 18 Feb 2003 23:16:11 +0000
Message-ID: <>

In message <b2uat1$f0t$>, Steve Kass <> writes

> 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

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.

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Received on Wed Feb 19 2003 - 00:16:11 CET

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