Re: More on view updates and inverse views

From: Marshall <marshall.spight_at_gmail.com>
Date: Tue, 8 Sep 2009 08:22:47 -0700 (PDT)
Message-ID: <2fcbd49a-40b6-44ec-952c-599245d2012d_at_t11g2000prh.googlegroups.com>



On Sep 6, 12:06 pm, Tegiri Nenashi <tegirinena..._at_gmail.com> wrote:
> Suppose we have views u, w defined as relational expressions over base
> tables x, y, z:
>
> u = f(x,y,z)
> w = g(x,y,z)
>
> Let's assume this system of equations is invertible, that is we can
> solve it and express x, y, z as functions of u, w:
>
> x = r(u,v)
> y = s(u,v)
> z = t(u,v)
>
> Then, the system of views u,w is updatable. Given the new database
> state reflected in the relations u, w, we can calculate base relations
> by leveraging above expressions. One can object that it wouldn't be a
> practical solution; on the plus side, however, increments and
> decrements never enter the picture!

It seems to me that whether a particular update will succeed on a particular
view depends not only on the view but on the specifics of the update operation as well. That is, whether an update will succeed or not is a dynamic, or runtime issue, and not a static, compile-time issue.

Marshall Received on Tue Sep 08 2009 - 10:22:47 CDT

Original text of this message