Re: Few confusing things about first normal form
Date: Wed, 22 Oct 2008 20:59:00 GMT
> 1) For DB to be in 1NF there must be no multi-valued attributes, and
> no repeating groups. When so, data is said to be atomic. ...
When Codd first used the word "atomic", he may have intended it very casually, as some of his intended audience were decision-makers, but (just as they often are today) many of those were non-technical people. It seems he was very much aware that no matter how good his idea was, it still needed to be sold.
CJ Date and like-minded people have discarded the term "atomic", saying it is at least imprecise and at worst meaningless as far as a Codd-ian relation is concerned.
They now like to use a more mathematical term - scalar. In their approach, in a the kind of relation Codd had in mind, the values of attributes are inherently scalar values. But many authors still natter on about atomic attributes. Maybe they are the kin of the 1960's secondary school teachers who were told to teach math from a set-theory perspective, never having been taught the latter themselves.
Anyway, Date and company's attitude might make one wonder if 2NF should be called 1NF, et cetera.
They discount "repeating groups" as well. As far as I can tell for the same reason. When Codd wrote his first papers, several hierarchical dbms's of the day as well as lower-level access methods had built-in support for such constructs. In fact I seem to remember that support had even found its way into Ansi Cobol. In his 1970 paper, Codd went out of his way to show that such a construct was redundant and therefore unnecessary.
Many in this camp also acknowledge the logical possibility of RVA's, relation-valued-attributes, at the same time as saying that the practical need for RVA's is rare.
Over the last hundred years or so, even the notion of atomic as being indivisible that physicists used has wandered, not just because it was discovered that atoms could be divided but also as more fundamental particles were discovered. Even before then, some had surmised that electrons might be jumping from atom to atom. Somewhere Date makes the point that data whose organization is expected to endure should be stored using durable principles. If the same goes for the lingo used, a mathematical noun/adjective seems better suited than a word like atomic that has so many nuances in common language. Received on Wed Oct 22 2008 - 22:59:00 CEST