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From: marti@ethz.UUCP (Robert Marti)
Newsgroups: comp.databases
Subject: Re: A few words on the "normaliztion"
Message-ID: <1664@ethz.UUCP>
Date: 31 Jul 89 06:47:54 GMT
References: <36270004@hpindwa.HP.COM>
Organization: ETH Zuerich
Lines: 25

In article <36270004@hpindwa.HP.COM>, donovan@hpindwa.HP.COM (Donovan Hsieh)
writes:
> [ ... ]  Above all, multi-valued dependencies are very difficult to
> formulate for the 4NF,
Huh?  I don't see what's so difficult about stating something like
empno -->> language (employees, identified by empno, have the ability
to speak/understand multiple languages).

> and it is also very expensive for the database system to enforce
> [the] multi-valued update consistency.
No DBMS enforces 4NF (or "multi-valued update consistency", as you call
it).  The database designer enforces 4NF, essentially by defining a
table per MVD.  Note that this is no differnet from 3NF:  The designer
enforces 3NF by defining appropriate tables and keys.

> A good database system design is more than just normalizing the tables into
> normal forms. There are various aspects of issues and problems involved
> in the design process which require special treatment and attention.
Yes.

-- 
Robert Marti                      Phone:      +41 1 256 52 36
Institut fur Informationssysteme
ETH-Zentrum                       CSNET/ARPA: marti%inf.ethz.ch@relay.cs.net
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