Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]
From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Thu, 16 Jun 2005 18:27:01 GMT
Message-ID: <Vvjse.122620$Vb7.6870078_at_phobos.telenet-ops.be>
>
> I looked at Ullman's slides and found a strange thing. I quote:
>
> Suppose we have relations ED, EO, EP, and DM,
> connecting employees to departments, phones, and
> offices, respectively, and departments to managers.
> [...]
> Consider a query "find the offices of employees
> managed by Sally."
>
> (End quote)
>
> Note that the relations do not say that *employees* have managers, just
> that *departments* do. Is it the case that an employee in a given
> department is always managed by the manager of that department? It is
> possible, even probable, but the database (as presented) does not say!
Date: Thu, 16 Jun 2005 18:27:01 GMT
Message-ID: <Vvjse.122620$Vb7.6870078_at_phobos.telenet-ops.be>
Jon Heggland wrote:
> In article <42b16163$1_at_news.fhg.de>, savinov@host.com says...
>>Jan Hidders schrieb: >>>For a very short explanation and a link to Jeffrey Ullman's sheets: >>> >>>http://app.deklarit.com/kb/article.aspx?id=10038&cNode=8J8X2Y
>
> I looked at Ullman's slides and found a strange thing. I quote:
>
> Suppose we have relations ED, EO, EP, and DM,
> connecting employees to departments, phones, and
> offices, respectively, and departments to managers.
> [...]
> Consider a query "find the offices of employees
> managed by Sally."
>
> (End quote)
>
> Note that the relations do not say that *employees* have managers, just
> that *departments* do. Is it the case that an employee in a given
> department is always managed by the manager of that department? It is
> possible, even probable, but the database (as presented) does not say!
- Jan Hidders