hitz@csi.uottawa.ca (Martin Hitz) (06/11/91)
In article <25200@oolong.la.locus.com> jfr@locus.com (Jon Rosen) writes: >In article <2421@ccadfa.adfa.oz.au> ghm@ccadfa.adfa.oz.au (Geoff Miller) writes: >> [...] >> However, you can implement a normalised data *model* in ways which use >> NFNF structures. > > This is do NOT understand... If you mean that you can use denormalization > for performance reasons after having appropriately normalized, I would > agree... Otherwise, I fail to see how the use of an NFNF model (which > I agree can be very useful in certain applications) can implement a > normalized view of the data, since these are essentially contradictory > views... Please explain... > > Jon Rosen Although I'm not Geoff and I can't tell what he meant, I remember that there are higher normal forms (2NF, 3NF) that have been generalized to NFNF models, so the "essentially contradictory view" arises only if one talks about 1NF in the context of NFNF (:-) Martin Hitz@csi.uottawa.ca
adw@otter.hpl.hp.com (Dave Wells) (06/21/91)
From: antoine@cl.bull.fr (Antoine Haraoui) >I have read some of the given definitions for a RDB. Actually those are rules >for designing an Entity/Relationship model rather than definitions. If we >are going to talk about normalisation so why not talk about integrity and >consistency rules... Indeed. >In my (and some others) opinion a RDB is : [definition deleted...] >go ahead and talk about first, second, third, Boyce-Codd, fourth, ... >normal forms. >As well as integrity and consistency rules... But then we will be >talking about a >totaly different subject; We will be talking about given a set of data, >how can we >have a good design to represent those data in a relational database. Indeed. Normalization is an attempt to use the structural (i.e. syntactic) constraints of a relation to capture as many semantic constraints as possible. By making it impossible to perform certain anomalous updates, you relieve your application code of the responsibility of forbidding them. As you say, these techniques are as applicable to arrays of records in a 3GL as they are to database tables. But there are obviously many constraints which cannot be so captured. "Only suppliers with warehouses in New Jersey may supply the Manhattan project". As DBMSs evolve to support more complex constraints like this, normalization theory will decrease in significance. Its not at all clear to me whether 4th or 5th normal form decompositions are "better" than BCNF relations (which can be derived from an ER model without knowing about normalization) in which the MV or join dependencies are expressed as separate constraints. Dave Wells