Re: does a table always need a PK?

Paul,

"Paul G. Brown" <paul_geoffrey_brown_at_yahoo.com> kirjoitti viestissä news:57da7b56.0308301443.21c98c43_at_posting.google.com...
> "Heikki Tuuri" <Heikki.Tuuri_at_innodb.com> wrote in message
news:<q593b.818$n62.433_at_read3.inet.fi>...
> > I have said that the concept of an 'RDBMS' is vague. Lee Fesperman and
Bob
> > Badour say it is not vague. It is their job to provide the exact
definition.
> > In the threads with Mikito Harakiri and Jan Hidders you find some
reasons
> > why I am asking these questions.
>
> This all boils down to the fact that what it is you mean by the term
> 'RDBMS' is not what Lee & Bob (et al) mean by 'RDBMS'. In common with a
lot
> of folk, you are using the term 'RDBMS' to refer to a class of server
> software which employs some variant of SQL and is used to manage data
> shared by application users. Bob, Lee and others use the term 'RDBMS'
to
> refer to an idealized product built in accordance to the principles
> of the 'relational model'.

surely you know that Codd's relational model is different from Date's relational model. Thus you should not talk about 'the relational model'.

> A DBMSs which deviates from the 'relational
> model' is not an RDBMS, by their reasoning.
>
> Now, although the relational model is not 'unambiguously' defined
> we can reason about each of its various flavors. Whether or not a
specific
> view is updateable, for example, is a question that can be decided
within
> any of the various relational models.

Well, I guess that in many models it is undecidable. That means there is no mechanical algorithm to decide if a view is theoretically updateable or not.

...
> So: your concept of an 'RDBMS' (and the concept used by Codd when
> formulating the Twelve Rules) is vague. But Lee & Bob's is not.

Good. Please show us where the concept used by Lee or Bob is formally defined. Lee talks about satisfying Codd's 12 rules. Where are the following formally defined?

http://www.cis.ohio-state.edu/~sgomori/570/coddsrules.html

"
9. Logical Data Independence
Application programs and terminal activities remain logically unimpaired when information preserving changes of any kind that theoretically permit unimpairment are made to the base tables. "

"
6. View Updating Rule
All views that are theoretically updateable are also updateable by the system.
"

"
3. Systematic Treatment of Null Values
Null values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type.
"

> It would be
> helpful if we all acknowledged that language itself can be ambiguous
> instead of assuming both the completeness and superiority of our own
> knowledge and slagging anyone who uses words differently.
>
> KR
>
> P "que the inquisition" b

Regards,

Heikki Received on Sun Aug 31 2003 - 08:23:42 CEST