Re: More on view updates and inverse views
Date: Tue, 08 Sep 2009 17:35:35 GMT
"Marshall" <marshall.spight_at_gmail.com> wrote in message
On Sep 6, 12:06 pm, Tegiri Nenashi <tegirinena..._at_gmail.com> wrote:
> 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)
PMFJI. I'm trying to combine this latest response with what Brian said in his latest response (about permitting NULLs in some attributes and providing default values in others.) Let me duck the issue of NULLS at least for the moment. Let's say that all attributes the base relvars and not in the projection have a default value. This makes the projection view "invertable" even though without the default value it would not be invertable.
So now my question is, can business rules such as default values (in the case of insert into projection) or triggers that implement a delete from join predictably and uniquely be expressed as "equations"? Is it possible that a system of equations that describe views in terms of base relvars and also describe business rules, including constraints, might always be "invertable". Well, it's more complicated than what I ve expressed, but I don't want to get all tied up in knots. The point is to ask whether there's always a way to make a non invertable system invertable by adding more rules.
> 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!
Received on Tue Sep 08 2009 - 19:35:35 CEST