Re: pro- foreign key propaganda?

Brian Selzer wrote:
... And by the way, I suggest you read Codd's book.
> Pages 89-90 describe the Update operator and the justification for it.
> ...
>
> I could cite other instances, but I think these sufficiently show that
> you're interpretation of Codd's use of the word 'update' is faulty.
> ...

That is a rather legalistic opinion of an informal, conversational sentence. Clearly, he is talking about an operator, not just a word. That aside, this is a topic that has often perplexed me.

To quote the start of that section: "In managing a database, it may be necessary occasionally to change the values of one or more components of one or more rows that already exist within a relation. This is usually distinguished from inserting entirely new rows because the components to be changed in value represent a very small percentage of the number of components in each row."

This strikes me as typical Codd pragmatism, also it is informal, really just about motivation, and he is hinting very strongly that 'update' should be fundamental (he doesn't mention delete before 'insert', as if 'insert' could mean wholesale replacement of the original relation). I don't object to pragmatism at all, but this paragraph jars with the one preceding it which is about insert and which specifically mentions set union as a way to think of insert.

Granted in advance that I am talking only of snippets from a longish book that has interleaved caveats and references among different chapters but I especially note the contrast of this chapter with the one on view updateability where he rejects certain updates as logically ambiguous, such as insert to disjoint views that don't have enough attributes to make the insert un-ambiguous logically. But how logical is it to suggest an update operator without saying that it is fundamental or providing an alternative definition, such as Date and Darwen do, that depends on additional notions, such as their "EXTEND"?

Maybe I'm misreading and Codd is really trying to avoid all ambiguities,eg., to protect data designers from themselves when they overlook the Information Principle but it seems to me that eg., it is just as logical (and pragmatic) to allow such an insert, distributed over the relations mentioned in a union view. Is the result of such an insert logically true? I think George Boole would have said yes, even if he might also say today that the intention of the user-designer combination is ambiguous as far as the dbms is concerned. (Regarding the recent mention of 'metrics', I've always liked binary ones, such as "does the user find the dbms's behavviour consistent?" or "is it intuitive?". I also noticed that Codd advocates that users should be aware of view definitions, contrary, I think, to D&D!)

(When if comes to implementations, I think that Codd is in basic harmony with D&D with his emphasis on "assignment". Also, it's been many years since I read that book all the way through and I was certainly even less competent then to read between the lines, so if anybody else wants to discount my reading, I'd be glad to hear that. Also, for those who are interested, acm.org lets you download this book for free, all you have to do is enable their 'free web' account.) Received on Sun May 25 2008 - 01:45:32 CEST