Re: History of 1NF

From: David Cressey <>
Date: Wed, 12 Mar 2008 19:14:11 GMT
Message-ID: <7YVBj.4180$Zo3.1320_at_trndny05>

"Marshall" <> wrote in message
> Back in the day, Codd originally defined First Normal Form
> (or maybe he was just calling it Normal Form back then)
> and proved something about it. Something about an
> isomorphism between nested relations and unnested
> relations? Could someone state specifically what he
> proved, please? And if anyone has a reference, that'd
> be good too.
> Thanks,

I don't know anything about the 1969 paper, other than its existence.

In the 1970 paper, he claimed and demonstrated that for any collection of nested relations, there is a collection of unnested relations that can express the same information. I'm not sure whether "can express the same information" is an isomorphism or not, but I think that is what you are driving at. He didn't use the terms "nested" and "unnested", but again I'm pretty sure we're talking about the same thing here.

He called the collection of relations with no nesting the "normal form" for that data. This term later became "1st normal form", when other normal forms were discovered. What he called a collection of relations is, I think, what you and I call a "schema". It's clear from the paper that normalization is not an absolute requirement for using the relational model of data.

I read a lot between the lines about what Codd's intent might have been in including and excluding various topics from the 1970 paper. This is thin ice. It is fair to assume that he was quite judicious about what to leave in and what to leave out. The paper covers an enormous amount of ground in relatively few words.

Here, I think that it might have been quite a lot easier to build the first relational database management system if one took the simplifying assumption that all attributes would be "simple" datatypes. (There have been a lot of arguments in c.d.t. about what makes a datatype "simple", but in the context of the paper, the term should be clear enough.) I think that Codd may have been raising the point about normalization in order to forestall arguments against building the first RDBMS based on the complexity of supporting nested relations.

His point is that even if you don't support nested relations, the schema designer is not limited by that in the expressive power of the system.

Anyway, this is my take on it. I never actually read the 1970 paper until after I started participating in c.d.t. You will remember a certain former participant who said that she had read the paper over and over again, and still didn't unerstand it. I was naive enough, at that time, to believe that I could help explain what Codd might have meant, and this would be helpful.

This is just my take on it. HTH. Received on Wed Mar 12 2008 - 20:14:11 CET

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