Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

"Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message news:KVz6a.16$i82.64_at_news.oracle.com...
> "Bob Badour" <bbadour_at_golden.net> wrote in message
> news:YcX4a.103$CO5.10014787_at_mantis.golden.net...
> > > Database A and B together can be viewed as a distributed database.
There
> > is
> > > a redundancy here: the data in both tables should be maintained in
sync.
> >
> > Strictly speaking, it's not possible to keep them in sync because a user
> can
> > insert a phone in phones without a fax. Contacts cannot represent this,
> and
> > what you claimed was a reverse mapping is not a reverse mapping.
>
> The view
>
> select id, 'VOICE' type, voice phone
> from contact
> union
> select id, 'FAX' type, fax phone
> from contact
>
> implies the following constraint
>
> For any 'id' and 'num' such that tuple
> <id, 'PHONE', num> is in the 'phones' view
> there exists 'num1' such that <id, 'FAX', num1> is in the 'phones' view as
> well.
>

That may be, but it does not match the predicate of the table it simulates in the other database, nor does the contact table have a predicate enforcing this. Received on Tue Feb 25 2003 - 08:43:46 CET