Re: Can we solve this -- NFNF and non-1NF at Loggerheads
Date: Mon, 7 Feb 2005 12:27:58 -0500
Message-ID: <36pmovF56om4aU1_at_individual.net>
"Paul" <paul_at_test.com> wrote in message
news:42079da8$0$34063$ed2e19e4_at_ptn-nntp-reader04.plus.net...
> Alan wrote:
> >> Roy Hann wrote:
> >>
> >>> 1NF does not "mean values are simple or indivisible". It just
> >>> says that for the purpose of the relational theory, the
> >>> divisibility (or internal structure) of values of a given type is
> >>> of no interest or use within the theory. The theory does not
> >>> make use nor reference to the internal structure of a value of
> >>> any type. The theory therefore does not need to define what
> >>> atomic means. The term "atomic" is a just a narrative short-hand
> >>> that Codd used to say, "That's stuff I don't care about, so
> >>> forget about it from now on as you read this paper." I can't
> >>> think of any other theory where a precise definition is demanded
> >>> for things that are *intended* not to be discussed. Plane
> >>> geometry isn't required to define colour for the purpose of
> >>> excluding it from discussion.
> >>>
> >>> There is nothing in RT that *prevents* values from being
> >>> divisible, there never was, and it would plainly be stupid to
> >>> want it that way.
> >>
> >> This sounds to me like an excellent summary of what "1NF" and
> >> "atomic" means. I can't believe we go round in circles discussing
> >> this point when it really is this simple!
> >
> > Okay, I will cite a well respected source supporting my position, then
you
> > do the same. From "Fundamentals of Database Systems, Third Edition",
> > Elmasri/Navathe, pages 485-487 Addison-Wesley, 2000:
>
> I don't see a conflict between the extract below and what Roy said
> above. Just that the text below is a bit on the verbose and practical
> side, and the above is a more abstract, concise and clear version.
And when I extracted the minimal amount of explanation in another thread, it somehow wasn't sufficient for you (or others, I forget). To me, the editors at Addison-Wesley, and countless university professors, it is perfectly clear.
>
> I don't think most of the people here actually disagree with the basics,
> just that there is a problem with expressing the ideas in written
> language such that they aren't misinterpreted.
>
> Paul.
>
> > "First normal form (1NF) is now considered to be part of the formal
> > definition of a relation in the basic (flat) relational model (Footnote
11:
> > This condition is removed in the nested relational model and in
> > object-relational systems (ORDBMSs), both of which allow unnormalized
> > relations.); historically, it was defined to disallow multivalued
> > attributes, composite attributes, and their combinations. It states that
the
> > domain of an attribute must include only atomic (simple, indivisible)
values
> > and that the value of any attribute in a tuple must be a single value
from
> > the domain of that attribute. Hence, 1NF disallows having a set of
values, a
> > tuple of values, or a combination of both as an attribute value for a
single
> > tuple. In other words, 1NF disallows "relations within relations" or
> > "relations as attributes of tuples." The only attribute values permitted
by
> > 1NF are single atomic (or indivisible) values. ...
> > The first normal form also disallows multivalued attributes that are
> > themselves composite. These are called nested relations because each
tuple
> > can have a relation within it..."
> >
> > Your _opinion_ is not solicited. Cite some facts from a published
source.
> >
> >
Received on Mon Feb 07 2005 - 18:27:58 CET