Re: insert to projection

On Sep 4, 12:12 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> Tegiri Nenashi wrote:
> > On Sep 4, 10:52 am, paul c <toledobythe..._at_oohay.ac> wrote:
> >> Tegiri Nenashi wrote:
>
> >> ...
>
> >>> The only RA operation, that seems to allow view updates is renaming.
> >> Since when does RA have views?
>
> > View is a named RA expression.
> > ...
>
> In other words, view is a language device.  RA has no ambiguity, so if
> your chosen dbms language allows ambiguous results, it is due to your
> choice of language,

Yes, guilty with sloppy language. The other thread has already established the term "underconstrained" rather than "ambiguous". So my thesis is that all simple relational expressions are underconstrained from view update perspective.

Let's get back to the main point. I'm suggesting that analysis of simple relational expressions update won't be useful. Suppose a view is composition of join, selection, and projection. Each of these can violate some restrictions that you would propose based on analysis of basic relation updates. Yet, the view can still be updatable. Received on Fri Sep 04 2009 - 22:26:16 CEST