Re: view updates (was something else)

NENASHI, Tegiri wrote:
> Aloha Kakuikanu wrote:
> [...]
> > What is a constraint? It is just some equation in relational algebra.
>
> Relational algebra is a very simplifee defintion of constraints because
> they do not explain database states. View updatability was attempted
> to be defined based on database schemata but not on states. It's
> precisement why the definition of updatability was not success.Temporal
> database or before/after update constraints are the same relational
> hack.
>
>
> > For some reason, view updates literature completely ignores a simple
> > fact that the problem is formulated not for a single view, but a set of
> > views. A single view changes often don't have enough information to
> > unambiguously solve the problem. In the above example we have 2 views:
>
> It is that what view updatability in the sketch model does. It says
> that the universal property we use is founded on the database states
> described with categorical morphisms that naturally describe states
> that relational algebra cannot describe You must read the article if no
> you will be lost in relational forest with its primitives. You read
> incorrect literature. Relational algebra is nice but it cannot explain
> dynamics like view update. You must learn category theory. Start with
> Zinovy DIskin works if the article which I advised is too hard or
> incomprehensible to you. The idea of state is adverse to the
> relational model, tout simplement.
>
>
> Bon chance
>
> --
> Tegi

You can find the definition about the states on my website: www.dbdesign10.com , definition 5.7. It is in fact based on the attributes (and the entities, the relationship...) It can be directly applied to RM without use of the category theory. I also don't thing that this story is part of the relation algebra, but I think that the relation model is the most natural and appropriated logical model for it.
Definition 5.8 is about the changes of states, definition 5.2 is about the attributes

Vladimir Odrljin Received on Sat Nov 04 2006 - 16:55:27 CET