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Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?

From: Aloha Kakuikanu <aloha.kakuikanu_at_yahoo.com>
Date: 7 Nov 2006 10:11:32 -0800
Message-ID: <1162923092.792306.315820@h48g2000cwc.googlegroups.com>


NENASHI, Tegiri wrote:
> Aloha Kakuikanu wrote:
> > This conclusion is unsatisfactory. The view is updatable.
>
> To complete my response that I gave before. I did not see that the
> union view that you gave had a element that is not in the database.
> The union view is a coproduct in the category language. Generally, the
> coproduct is not updatable but if one injects an element that is not in
> the database like one of the legs of the coproduct, it will be
> updatable. The universal property of updatability that the functor
> F:Mon(V)==>Mon(E) must be left and right fibration is honored. The
> proof is easy. Like I recollect the SQL union is never updatable.

Oh, phlease. Sampo already gave you a reason why category theory is wrong abstraction level for the database theory in general.

I will have no difficulty producing subtle variations of the problem that would escape your formalism. Here we go:

  1. Is the view

select name, 'U' from (
  select name from RealPeople
  union
  select name from Impostors
)
union
select name, 'I' from (
  select name from RealPeople
  intersect
  select name from Impostors
)

updatable?

2. Is the view

select name, 'RMI' from (
  select name from RealPeople
  minus
  select name from Impostors
)
union
select name, 'IMR' from (
  select name from Impostors
  minus
  select name from RealPeople
)
union
select name, 'I' from (
  select name from RealPeople
  intersect
  select name from Impostors
)

updatable?

BTW notice that before I was talking about updating a system of views (similtaneously). A simple extension operation combines a system of views into a single view, as you see from the above examples. Received on Tue Nov 07 2006 - 12:11:32 CST

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