Multiple-Attribute Keys and 1NF

#91

On Sep 1, 2:31 am, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote:

Quote:

"David Cressey" <cresse... (AT) verizon (DOT) net> wrote in message

news:UfUBi.12075$Eh5.9962 (AT) trndny06 (DOT) ..

"JOG" <j... (AT) cs (DOT) nott.ac.uk> wrote in message
news:1188556656.192653.305160 (AT) r23g2000prd (DOT) googlegroups.com...

Well I've never suggested multiple values contained in a collection.
But yes as I said, multiple roles does break the guaranteed access
rule. My question is now (in the continuuing hunt for the theory
behind 1NF) is why on earth would that be a problem? I don't see any
affect on the relational algebra.

I honestly think that the impetus behind "normalization" in the Codd 1970
paper is more of a stopgap than a theory. (I'm not familiar with the
1969
paper, and I only read the 1970 paper after I began participating in the
discussions in c.d.t.) In the 1970 paper, Codd suggests that it may be
worthwhile to consider the subset of schemas that contain only atomic
attributes. (He didn't use the word "schemas", but I hope I can use it
without introducing confusion.)

The whole point of 1NF boils down to the following two sentences from the
June, 1970 article: "The adoption of a relational model of data, as
described above, permits the defelopment of a universal data sublanguage
based on an applied predicate calculus. A first-order predicate calculus
suffices if the collection of relations is in normal form." Therefore, the
impetus behind "normalization" is to model the universal data sublanguage
after a first-order logic rather than some higher order logic.

That's a great quote - probably the best reasoning i've seen for 1NF.
Thanks.

Quote:

He pointed out that such a restriction did not thereby reduce the
expressiveness to the system, in that for every unnormalized schema,
there
existed an equivalent normalized schema. "normalized" in the 1970 paper
is
called 1NF in later writings, once further normal forms were discovered.

There is one other piece of the 1NF definition in the 1970 paper, the "no
duplicates rule". The no duplicates rule has to do with the
representation
of a relation, and not with a relation itself. Codd imagined (correctly)
that the first relational database systems would use records to represent
tuples and (virtual) arrays of records to represent relations. In a
relation, there is no such thing as "a tuple appearing twice". However,
in
an array of records, there is such a thing as two of the records having
identical contents. Codd ruled that out as a practical stop gap, in
order
to prevent the implementations from diverging from the properties of
mathematical relations in an unnecessary and harmful way. This is my
reading of the 1970 paper, in regard to 1NF theory.

There's a connection between the "atomic values" rule and the "no
duplicates
rule", at the implementation level.

consider the following fact:

Jack speaks English and German.

Let's say we are about to include this fact in a relation stored somewhere
in a relational database, and that one of the columns of a relational
table
is "set of languages spoken".

Further, let's say that there is already a tuple in the relation with the
following fact stored:

Jack speaks German and English.

As a practical matter, in terms of the representation of data inside a
database, it can be extraordinarily difficult to ascertain that these two
propositions, together, violate the "no duplicates rule"

Notice that my focus has been entirely on the implementation, and not on
the relational algebra itself. With regard to the relational algebra
itself, I believe your understanding is correct.

So what the heck are implementation oriented issues doing in the 1970
paper?
I believe Codd wanted to get across two main ideas: building a system for
relational databases would be a good idea. And building such a system was
also feasable. It's for this second reason that I believe Codd added some
material that is primarily about implementation, rather than about the
power
of relational algebra itself.

This is my insight, such as it is. I hope it helps.

#92

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote

Quote:

"David Cressey" <cressey73 (AT) verizon (DOT) net> wrote in message
news:UfUBi.12075$Eh5.9962 (AT) trndny06 (DOT) ..

"JOG" <jog (AT) cs (DOT) nott.ac.uk> wrote in message
news:1188556656.192653.305160 (AT) r23g2000prd (DOT) googlegroups.com...

Well I've never suggested multiple values contained in a collection.
But yes as I said, multiple roles does break the guaranteed access
rule. My question is now (in the continuuing hunt for the theory
behind 1NF) is why on earth would that be a problem? I don't see any
affect on the relational algebra.

I honestly think that the impetus behind "normalization" in the Codd
1970
paper is more of a stopgap than a theory. (I'm not familiar with the
1969
paper, and I only read the 1970 paper after I began participating in
the
discussions in c.d.t.) In the 1970 paper, Codd suggests that it may be
worthwhile to consider the subset of schemas that contain only atomic
attributes. (He didn't use the word "schemas", but I hope I can use it
without introducing confusion.)

The whole point of 1NF boils down to the following two sentences from the
June, 1970 article: "The adoption of a relational model of data, as
described above, permits the defelopment of a universal data sublanguage
based on an applied predicate calculus. A first-order predicate calculus
suffices if the collection of relations is in normal form." Therefore,
the
impetus behind "normalization" is to model the universal data sublanguage
after a first-order logic rather than some higher order logic.

Thank you, Brian. This clarifies the issue enormously for me.

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Multiple-Attribute Keys and 1NF

comp.databases.theory comp.databases.theory

Re: Multiple-Attribute Keys and 1NF - 09-01-2007 , 05:21 AM

Re: Multiple-Attribute Keys and 1NF - 09-01-2007 , 07:17 AM