Re: Date's First Great Blunder

From: Tony <>
Date: 14 Apr 2004 04:57:51 -0700
Message-ID: <>

"Dawn M. Wolthuis" <> wrote in message news:<c5ia56$t04$>...
> C. J. Date has written about what he calls "The First Great Blunder" related
> to this question: What concept is it in the relational world that is the
> counterpart to the concept of object class in the object world?
> He suggests that there are two answers given: domain = object class or
> relvar = object class. He then says that the first equation is obviously
> right and the second wrong. Classes are types and domains are types, but
> relvars are variables and, therefore, not types, so QED.
> The idea, it seems, is to rid Java programmers of the notion of using
> classes to define "relations" or records. I'm guessing I'm not the only one
> who doesn't buy Mr. Date's argument.

You'd be right, it goes against the grain for many OO folks.

> I'll toss out one of the way-too-many-thoughts buzzing in my head on this
> topic. How about this equation:
> Class = Metadata
> A class is a spec/template -- not a variable nor an object. There can be
> metadata for a type and metadata for a relation/record and classes
> corresponding to either.
> Do many folks agree with Date on this point or is this one of his
> lone-ranger attempts to push against the OO folks? --dawn

I agree with Date - when I first saw him present this at a seminar back in 1997 it struck me as a obviously true, once pointed out. But it isn't really an attack on the OO folks, rather it is a defence of the relational model AGAINST attacks by the OO (or OR) folks, who have said that the relational model is at fault and should be fixed by the "relvar = object class" approach. However, it is true that in the process of doing that, Date has pointed out flaws in the thinking behind OO - flaws which he very much wants to keep out of the relational model! Received on Wed Apr 14 2004 - 13:57:51 CEST

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