Re: Help! I can't support normalization

>
>
>>It proposes a table called TableNum with just one column containing
>>integers from 1 to ....
>>It also has some proposed applications.
>>
>>Now, would such a table be a virtual or a real one??
>>
>>
>
>Well, it depends what you man by "real". In a sense all tables are
>virtual because they are purely logical constructs. But what would it
>mean say to delete a row from such a "domain relation"? Really it
>shouldn't be allowed.
>

I wouldn't call it a "domain relation", just a relation like any other one.

>I guess what you're meaning is that we would have two categories of
>table: ones where the rows are listed explicitly and ones where the
>rows are defined in some kind of induction process. These second sort
>of tables you could only SELECT from, as INSERT, UPDATE, DELETE might
>not make sense. Or maybe they would? Say I wanted to change my
>integer domain to be all integers (within a certain range) excluding
>"13"? Should I be allowed to do this or should the "built-in" domains
>remain as they are and I should define a new domain based on, but
>separate to, the integer domain (type inheritance?)?
>

Well, I think that TableNum is a special case. As for excluding '13' all you have to do
is 'select N from TableNum where N <> 13'

My opinion is that relations and domains are basically different things.  Both are needed but
they suffice.

The "real world" is like a piece of soap: when you try to completely model it, it just slips from your
hands. So what is a relation and what is a domain really depends on what angle
of the "real world" you are taking.

The concept of 'color' could be a domain in one application (say a product catalog), but
in a paint-factory it would probably consist of several relations (anybody know,
by the way?)

I quote from Date: Introduction to Databases (7ed) pages 66-67:

  -Types [=domains] are (sets of) things we can talk about

• Relations are (sets of) things we say about the things we can talk about

[...]

  Types [=domains] are to relations as nouns are to sentences

>
>I've only briefly read about them but is this moving towards things
>like constraint databases?
>
>Does this violate Codd's principles? Should all relations be able in
>theory to be manipulated by any SQL DML statement?
>

I wouldn't think so. Why would it?

regards,
Lauri Pietarinen Received on Wed Nov 20 2002 - 15:22:17 CST