# 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:

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