Re: So let me get this right: (Was: NFNF vs 1NF ...)

On 10 Feb 2005 10:29:06 -0800, "DBMS_Plumber" <paul_geoffrey_brown_at_yahoo.com> wrote:

>Alfredo Asks:
>
>>> "Where Codd said that relational valued attributes are not [OK]"
>
>>From [1]
>
>"The term relation is used here in its accepted mathematical sense.
>Given sets S1, S2, ... Sn (not necessarily distinct), R is a relation
>on these n sets of it is a set of n-tuples each of which has its first
>element from S1, its second from S2, and so on. {FN1}"
>
>{FN1} "More concisely, R is a subset of the Cartesian product S1 x S2 x
>... x Sn."
>
>Now, what is the "accepted mathematical sense." of a "relation"? Well,
>to be sound the "mathematical understanding" should be free of
>paradoxes, and contradictions. As soon as you start saying "the set of
>domains includes sets of sets" or the like, you leap headlong into a
>twisted maze of paradoxes.

RVAs don't lead to any paradox.

> Consequently I propose that in the original
>paper Codd ruled out the possibility that the values in an attribute
>could be considered as amenable to manipulation via the "Operations on
>Relations" he describes in Section 2.1.

You have to "extract" a relation attribute value before operating with it.

>> But bag data model makes rutime far less efficient.
>
> Evidence?

http://www.dbdebunk.citymax.com/page/page/638922.htm http://www.dbdebunk.com/page/page/638922.htm

>What you've stated is the opposite of what early systems builders
>concluded.

Early systems builders made many mistakes.

>(Note: I ain't sayin' either way. I'm just sayin' the case is far from
>clear. This is an empirical question, not a theoretic one.)

This is a rather clear theoretic question.

>You are quite correct: I mis-remembered. The only requirement is
>"equals" as far back as [1]. However, the object-relational crowd
>allowed scalar domains which do not even have equals. That's just fine
>from a data modeling perspective, so long as those domains are never
>used in a key. But even that would be outlawed by the 3rdM
>"interpretation".

I don't see any sense in a domain of values without identity.

>> But it needs correct interpretation.
>
>Any my point is that you appear to believe that Date, Darwen & Pascal
>have a unique ability to "correctly interpret".

Not unique, but I don't know better authors than they.

BTW I don't agree with them in everything. For instance I am against the principle of orthogonal design, the view updating rules, transactions as a prescription of the RM, I am becoming very skeptical about the TransRelational Model, etc.

>My challenge to you is to find one single, stinkin' thing anyone else
>has ever written about the relational model of which the Date / Darwen
>crowd approved.

There are many examples in the bibliography of their books.

For instance Fagin's works about functional dependencies.

Regards Received on Sat Feb 12 2005 - 13:08:58 CET