Re: Codd and many-valued logics

On 2016-06-01 02:12:15 +0000, -CELKO- said:

> I also do not remember Codd referencing prior multivalue logics.
> However, D David McGovern spend some time on this topic. It will be
> worth googling it. I also posted things on this decades ago. David's
> work is much much better than mine. He points out of a full logic has
> to have conference rules.

Thanks, I have found his Nothing from Nothing series of articles.

> In SQL we have search conditions and resolution rules for the searches;
> not the same thing exclamation

Sure. From a theoretical point of view, though, one may legitimately wonder about the relationship between SQL with nulls and 3VLs in the same way as we know the relationship between SQL without nulls and classical logic, at least for a fragment of SQL. Both McGoveran and Date (well, mostly the former, since the latter is just repeating McGoveran's arguments) are too dismissive in my opinion, e.g., they do not even consider first-order 3VLs. There are at least a couple of papers formalizing the semantics of SQL with nulls by extensions of relational calculi or algebras, so the question of the expressive power of such extensions compared to the 3VLs in the textbooks is well defined (the problem of giving an *intuitive* interpretation of such logics is another matter).

Coming back to my initial question, I am wondering whether Codd deliberately avoided citing works about many-valued logics for fear that his proposal would be considered too abstract for serious consideration by implementors.

Nicola

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