Re: Another motivational example for inverse view

From: NENASHI, Tegiri <tnmail42_at_gmail.com>
Date: Thu, 16 Nov 2006 21:28:43 +0100 (CET)
Message-ID: <Xns987D9D8A3319Casdgba@194.177.96.26>

"Aloha Kakuikanu" <aloha.kakuikanu_at_yahoo.com> wrote in news:1163634954.665108.258580_at_k70g2000cwa.googlegroups.com:

> NENASHI, Tegiri wrote:

>> You are joking are you not ?  It is simple because the structure of
>> the relations is the same,  there is not the change of the structure
>> that a join of tables has,  you did not create a new structure.  The
>> probleme of the view updatability is a morphing of one structure into
>> the other.

>
> Yes the relational transformation is indeed simple in this case. Yet
> the example is far from trivial. And the quesion is: how do one
> formally inverts such a view.
>

One uses the properties of the structure, the relational schema, to determine if the view is updatable. The example of coordinates, it is of a different kind. The likeness is on the surface only. One must know the direct and inverse mappings and so long as one knows, it is a trivial task. The database system does not know the mind of the programmer and the database system can not transform the coordinates. Received on Thu Nov 16 2006 - 14:28:43 CST