Re: Lucid statement of the MV vs RM position?

"JOG" <jog_at_cs.nott.ac.uk> wrote in message news:1146525657.263941.305480_at_v46g2000cwv.googlegroups.com...

> I'm confused by this statement Dawn. My understanding is as follows:
>
> 1NF is definitional in that it is simply a case of saying that
> "everything must be stored as tuples", allowing sets of such to form
> relations. By definition, mathematical relations may not have variable
> cardinalities across tuples and hence (but only as a consequence)
> applying 1NF means that each field must be guaranteed to occur but
> once.
>
> However, an element in a tuple may happily be a set, a list, a RVA or
> whatever user defined type one wishes to use and still be 1NF, as one
> can still form acceptable tuples with them. Currently one has to
> manipulate these user defined types externally as the tools aren't
> really there to do otherwise (apart from strings and date types).
>
> Is this not how you see it? All best, J.

This newsgroup has been down this trail many times before.

In Ted Codd's 1970 paper, he points out that when a system of relations is devised to store a body of facts, there are other systems of relations that will express precisely the same body of facts. He then points out that within a group of such systems that are all logically equivalent, there will be (at least) one that contains no sets, lists, or RVAs as elements of a tuple.
He called that the normalized form for the group. Later on, when 2NF was discovered, "normalized" got renamed to 1NF.

In c. 1992, C.J.Date redefined 1NF to permit RVAs as elements. Not everyone follows Date's definition. In particular, some introductory material to the RDM still teaches 1NF, 2NF, and 3NF as they were defined in the 1970s and 1980s.

I hope the above summary can save a few iterations in the newsgroup. Received on Tue May 02 2006 - 13:06:01 CEST