Re: Can we solve this -- NFNF and non-1NF at Loggerheads

From: Paul <paul_at_test.com>
Date: Mon, 07 Feb 2005 18:12:50 +0000
Message-ID: <4207afa3$0$55486$ed2619ec@ptn-nntp-reader02.plus.net>

Alan wrote:

>>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.

>
> Then you better re-read the "more abstract, concise, and clear" inaccuracy
> that Paul wrote. Here, I'll make it easy:
>
> Paul:
> "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."

(just to point out these words were Roy's, not mine, though I agreed with them)

> Alan, via Elmasri/Navathe:
> "...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..."
>
> There is no way to interpret other than how it was written.

I think the misinterpretation is over what model or universe of discourse we are discussing. The first quote is saying that values are atomic or indivisible from the point of view of the relational part of the RDBMS. But it's saying they could be divisible in some much larger model of which the relational model is but a small part. And that this is outside the scope of the relational model, so we ignore it.

As someone else said in another thread:

Chemistry: atoms are indivisible!
Physics: atoms are divisible!

neither are wrong, they are just looking at things from a different perspective.

> What Paul and everyone else is talking about, but can't articulate, is that
> there is another theory/model, with the (in?)formal name of "Nested
> Relational Model", or NFNF (Non First Normal Form). This is the model/theory
> where the restriction of 1NF is _removed_, not redefined (Elmasri, page
> 459).

I think there are 3 models:

1. Standard Codd-style relational model based on pure first-order predicate logic, where relation-valued attributes are only allowed if the relational operators in the DBMS don't know they exist. To look inside them requires domain operators.
2. Date's amended relational model, where relational-valued attributes can exist, and additional relational operators are introduced to enable the DBMS to look inside these relational-valued attributes.
3. A Pick-style model (often called "non-first normal form" or NFNF), which essentially enables any attribute to be a list of values (I think). I'm not so familiar with this but I think that instead of a row repesenting a proposition like this:

   PERSON has tel no TEL and email address EMAIL

it represents propositions like this:

   PERSON has tel nos [TEL1, TEL2, ...]
     and email addresses [EMAIL1, EMAIL2, EMAIL3, ...]

where I think these are ordered lists (correct me if I'm wrong)

>>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.

>
> Nonsense. Of course they disagree, that's what we've been arguing about.
> I've cited well-respected, published proof of my argument, and until someone
> can present well-respected published proof (and not just on the internet
> where one could find "proof" of little green men from Mars) of their
> argument, they should keep quiet. Or apologize.

I don't think this is the kind of question that admits a "proof" unfortunately - it's all about how things are interpreted.

Paul. Received on Mon Feb 07 2005 - 12:12:50 CST