Re: How to find Brothers and Sisters?
Date: Mon, 04 Dec 2006 20:12:51 GMT
> Cimode wrote:
>>David Cressey a écrit : >> >> >>>"Cimode" <cimode_at_hotmail.com> wrote in message >>>news:1165242357.899497.161570_at_j44g2000cwa.googlegroups.com... >>> >>> >>>>>I would think this is more a design flaw than the table not formally >>>>>being in 1NF. No repeating groups. check. Data in the form of a >>>>>relation. check. Some root entry in 'persons' who has himself or one of >>>>>his successors as a father... erm.....hold on... >>>>> >>>>>(I think that Marshall once pointed out that the technical term for >>>>>this is Furturama-NF, where Fry is his own grandfather) >>>> >>>>Repeating groups is not the only prerequisite to state a table is in or >>>>is not in 1NF. >>> >>>>There is no way you can be in 1NF if NULL values are permitted OR if >>>>you have 2 different predicates in the same RTable...Only one predicate >>>>per RTable.. That's by definition. Period. >>> >>> >>>Where did you get that definition? >> >>Check... >>06/03 #2: WHAT FIRST NORMAL FORM MEANS NOT by F. Pascal (Updated 03/04) >>06/03 #1: WHAT FIRST NORMAL FORM REALLY MEANS by C. J. Date
> couple of things. First, It annoys me these papers are not publically
> available. I understand one needs to earn a crust, but these seem
> fundamental issues and as such, it would be nice to see them out in the
> Second, as far as I am concerned 1NF requires data that fits into a
> relation. Hence no nulls or repeating groups. However, given Codd
> invented 1NF and was (in)famously a proponent of nulls, I am uncertain
> that the currently accepted definition of 1NF yet precludes them. This
> is sad of course, but we are still subject to these definitions, even
> though we promote their change.
> Third, there may be some confusion between schema and semantics. While
> the supplied table allows a nullable column, and hence should not be
> 1NF (although by many definitions including Codd's it is), this is
> wholly different from the knowledge we have that everyone must have a
> father. The latter is the design flaw I am referring to and it is
> important not to confuse the two in your answers to the OP.
While the proper treatment of missing information is problematic and subject to considerable controversy, I do not recall that Codd's original specification of 1NF allowed NULL.
Codd's RM/V2 had lots of stuff that a lot of people would find controversial or would leave a lot of folks scratching their heads. Received on Mon Dec 04 2006 - 21:12:51 CET