# Re: More on view updates and inverse views

Date: Sun, 06 Sep 2009 19:29:39 GMT

Message-ID: <D4Uom.44008$PH1.7319_at_edtnps82>

Tegiri Nenashi 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!
*

I think as soon as one starts using functions to describe relations it's easy to loose track of important details. In the above u=f(x,y,z) could result in a an rva, If I understand what you're saying, to invert it, you'd have to back and make x an rva too but once you do that u becomes a kind of nested rva and you'll recurse forever!

Also, if one accepts that relational assignment is really what 'update' means, increments and decrements don't enter the picture in the first place. . Received on Sun Sep 06 2009 - 21:29:39 CEST