Re: On view updating

mAsterdam <mAsterdam_at_vrijdag.org> wrote in message news:<41553835$0$559$e4fe514c_at_news.xs4all.nl>...

> The consequence is that many lengthy misunderstandings
> can be avoided by immediately giving a clear
> definition of some crucial terms whenever used
> in a discussion which goes beyond one of those groups.
> Define it for the discussion at hand.
> My hope is that new, more broadly used definitions
> will arise.

I agree. Fortunately we have dictionaries and institutes of standards.

> My statement asserts several things in one go,
> but most importantly: that 'type' is one of the
> words that has its meaning bend and twisted
> (jargonised) subtly differently in different
> groups. I call it a non-problem, because I suspect
> the jargon differences cover up some real,
> perception of subjectmatter related (instead of
> just the labeling), interesting problems.

My obvious sugestion is that we should resort to the authoritative references:

http://www.nist.gov/dads/HTML/abstractDataType.html

> > They are intended to be shorthands for expressions, but they are not
> > syntactic shorthands because they are database objects. Views exist in
> > the database catalog.
>
> Syntactic shorthands cannot exist within the database catalog?

No, it makes no sense. A syntactic shorthand is only an alternative and shorter way to say something, and not an alternative way to achieve a desired result.

> > Both groups of statements have different semantics therefore a view is
> > not a syntactic shorthand.
>
> If the deletion of 'r where a > 10' is a common thing to do,
> then var v makes database A easier in use than database B.

Indeed, not all shorthands are syntactic.

> Assuming var r has the same semantics and values in both databases,
> both databases reflect the same facts.
> This is true before and after the deletes.

Indeed, but the statements have different meanings, and syntactic shorthands only affect to the syntax, and never to the meaning.

For instance:

a := a + 5;

is not a syntactic shorthand for this:

for i := 1 to 5;
  a := a + 1;

The result is the same, but we are not saying the same.

> > delete a union b;
> >
> > or
> >
> > var r relation { a integer }
> > key { a }
> > foreign key { a } references a union b;
>
> This puzzles me. From 'delete a union b;' I took the suggestion
> that a and b where both relational variables.

Yes.

> In the second
> statement a is a declared integer in the first line,
> and what is a in the tail of the 3rd line of the second statement?

The same relation variable as in 'delete a union b'.

In relational databases is frequent to have relvars and attributes with the same name, but I should have used a different name, sorry.

Regards Received on Sun Sep 26 2004 - 01:00:49 CEST