Re: On view updating
From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sat, 25 Sep 2004 14:12:17 +0200
Message-ID: <415560a1$0$43451$e4fe514c_at_news.xs4all.nl>
>
> There's no such thing as "virtual variables" in PL theory.So to avoid
> confusion by "my imaginary model" vs. "your imaginary model" kind of
> debate let's enumerate some invariants across all reasonable models
>
> - Views have a name
> - A view denotes an expression that can be evaluated or composed with
> other expressions.
> - views do not denote a "store".
>
> as opposed to views, tables, which also have a name:
>
> - denote a "store". A place in the global state holding a value that can
> be changed.
Date: Sat, 25 Sep 2004 14:12:17 +0200
Message-ID: <415560a1$0$43451$e4fe514c_at_news.xs4all.nl>
Costin Cozianu wrote:
>>> Since relvars are "variables" and the rest are computed values, >> >> Views are variables too. Virtual variables but variables. Although a >> "closed view" has nothing of virtual to the user.
>
> There's no such thing as "virtual variables" in PL theory.So to avoid
> confusion by "my imaginary model" vs. "your imaginary model" kind of
> debate let's enumerate some invariants across all reasonable models
>
> - Views have a name
> - A view denotes an expression that can be evaluated or composed with
> other expressions.
> - views do not denote a "store".
>
> as opposed to views, tables, which also have a name:
>
> - denote a "store". A place in the global state holding a value that can
> be changed.
A store, which is completely hidden from the users of the table (encapsulated by the RDBMS). To the user, the table poses as store.
> Therefore, here you have your trivial distinction in all imperative
> languages between a "store" (variable, possibly aliased or non-aliased)
> which is your lvalue, and an expression.
Why could a view *not* pose as store?
Hey! You just invented the 'virtual variable'!
:-) Received on Sat Sep 25 2004 - 14:12:17 CEST