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

Dan wrote:

...
> Here we go:
>
> First Normal Form: A relvar is in 1NF if and only if, in every legal value
> of that relvar, every tuple contains exactly one value for each attribute
> (Date, 7th ed. p. 357).
...

not trying to put words in anybody's mouth, but doesn't it hinge on what we mean by 'value'?

a value might be a character, a set of characters or a set of sets of numbers, or a bag of ordered characters, but it could be many other things too. if we accept that domains are essential in a model, then wouldn't the domain's implementation represent the definition of a value in the context of the domain?

and a value could be seen many other ways.

not trying to be all-encompassing about this, but i detect that values can be slippery things, just as slippery as 'nulls'. i wonder if the notion of equality isn't also part of this discussion.

for example, a 'jpeg' domain might say that two images are equal if they contain my face even if the other faces aren't the same. somebody else might use the same database with a different domain to assign equality based on their face. so the two databases might be the same in some mechanical sense, but give different answers. maybe that's a stupid example but i think it makes my point.

there seems to always be a tension between the philosophical and implementations. for example, it's just not true that a mechanical interpreation of 'bit content' can decide what everybody means by equality in every possible sense - i knew one product that refused to let you decide equality of an integer and a float on the grounds that floats (at least as they are represented in computers) are approximations. the thinking went: "how can you compare the approximate to the exact?".

maybe i'm veering off topic but some of you may be interested in this link that discusses "what is a null". it's at http://www.marmaladesky.co.uk/~adrianlarner/database.htm#paper along with some other provocative stuff. IIGIR, the writer doesn't seem to answer "what is a value", except in practical terms, ie. it is the answer to a question on a form!

apart from that, i always have a problem with the above "tension". can't quite swallow the word 'model'. after all, everybody knows that a computer doesn't duplicate reality, just represents some aspect of it.

   even if the computer reflects our meaning, how do we know that our intelligence models reality?

pc Received on Tue Feb 08 2005 - 18:53:31 CET