Re: On view updating

mAsterdam <mAsterdam_at_vrijdag.org> wrote in message news:<41540767$0$568$e4fe514c_at_news.xs4all.nl>...

> > Reference (pointer) types don't exist in relational databases.
>
> Forgetting this (by DBMS vendors even) has led to many problems.
> Remember the pointer/FK "discussion" a while ago?

Indeed, but this is a very basic principle.

> Both that deceptively simple looking overloading of the
> 'type'-concept, and (D&D's) in some ways similar attempts
> to reduce 'object' to 'type' lead to many vocabulary based,
> camp generating non-problems.

I don't understand this.

> > Non sequitur. Of course views are not a syntactic shorthand.
>
> What if they are syntactic shorthands - as long as it is clearly
> defined what they are shorthands for, I don't see a problem?

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.

For instance:

Database A:

var r relation{ a integer } key { a };
var v view r where a > 10;
delete v;

Database B:

var r relation{ a integer } key { a };
delete r where a > 10;

Database A has two defined variables while Database B has one. Both databases are different.

Both groups of statements have different semantics therefore a view is not a syntactic shorthand.

A syntactic shorthand is something like this:

a++;

This is a syntactic shorthand for:

a = a + 1;

Both statements have identical semantics.

BTW here it is clear that we can delete from a relational expression: (r where a > 10), so relational expressions are nameless variables, and we can update relational expressions without using views.

A view is an expression and a variable at the same time.

This could be a legal syntax in a relational language:

delete a union b;

or

var r relation { a integer }

    key { a }
    foreign key { a } references a union b;

Regards Received on Sat Sep 25 2004 - 02:06:13 CEST