Re: Which normal form is this violating?
Date: Mon, 29 Apr 2002 10:07:23 +0200
Message-ID: <3cccff99$1_at_news.uia.ac.be>
<paul.vernon_at_ukk.ibmm.comm> wrote in message
news:aac5se$12lq$1_at_sp15at20.hursley.ibm.com...
> > SQL prevents you from having two tables with the same names, but
> > relational theory says that since a table is a set, it can appear only
> > once in a schema, no matter what the name.
>
> I have wondered about this one. Does the theory really say that you are
> not allowed two relations in a relational database that differ only by
> name?
No, the theory says no such thing. The reasoning above makes two mistakes. First, it assumes that a database scheme contains relations, but it is the database *instance* that contains relations, the scheme only describes them. Secondly, a database instance is not a set of relations but more like a tuple of relations, and as you probably know a tuple can contain the same thing several times.
- Jan Hidders