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

Alan: "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.

Note: please refer to inclusive thread for further context.

Alan,

I have the Elmasri/Navathe text at home as well; and I use it as my primary reference of choice along with Date's "Introduction...". I think the definition provided by them is totally valid.

However, the definition doesn't really address the issue of how we use symbols and languages to communicate meaning. This is left up to the user to manage and dictate to a system. A phone number in one sense is totally atomic in that it is an address for reaching someone by telephone. If this definition suites the user's needs in terms of retrievability using RT, then it is atomic by the user's standards. However, if a user is going to join area codes with geographic cities, then it makes sense that the "database" will have a need for a decomposed variant of telephone number.

I think this case is more common than we actually appreciate. And if we want to take it in the extreme, there might actually be users who are interested in asking questions such as which employees have a home phone number where the second digit in the area code is equal to the fifth digit of his or her social security number? What do we end up with in such a case? Well, Neo's experimental database of course! <g> However, decomposing to such an extreme poses real practical limitations. Other methods, such as type operations, can do these quite effectively without producing a model so mired in minute details that the general concepts are totally occluded.

A while back I produced a reference in response to Dawn that quoted Codd on his intent concerning the meaning of "atomic" as it applies to RT. Parenthetically, he qualified the use of atomic with the clarification, "not further decomposable by the database." I can reproduce the reference if you wish, but I'm hoping you might remember.

I interpret this rather succinct footnote to mean that an element which is entirely decomposable in every sense of the word is a sufficient condition for 1NF, but it is not a necessary condition. The necessary codition comes from the words, "by the database" (and the designer who designs it).

Does this make sense?

Regards,

Dan Received on Mon Feb 07 2005 - 20:03:55 CET