Re: On view updating
Date: Fri, 24 Sep 2004 13:39:08 +0200
Message-ID: <41540767$0$568$e4fe514c_at_news.xs4all.nl>
Alfredo Novoa wrote:
> Costin Cozianu wrote:
>>* value types and reference types are distinct
>
> Reference (pointer) types don't exist in relational databases.
Forgetting this (by DBMS vendors even) has led to many problems. Remember the pointer/FK "discussion" a while ago?
>>(l-values are distinct from r-values)
>
> Or course!
>
> This is a confusion prone bad terminology. l-values are variables and
> r-values are values (sometimes placed in variables).
>
> http://faculty.juniata.edu/rhodes/lt/datatypes.htm
>
> I will not use that terminology.
I said it a while ago, I'll say it differently now: IMHO only the *defining* operators should participate in any definiton of a type. Other operators do *not* belong there. This is in line with a well established tradition. A good example is Peano's definition of Natural numbers based on the successor operator.
'plus', 'minus' and what have you operate on natural numbers, but they are *not* part of the definition of natural numbers.
http://en.wikipedia.org/wiki/Peano_postulates
> ... With tables some of the assignments will fail because they violate
> some integrity constraints. With views some assignments will fail for
> the same reason and other will fail because the DBMS does not know how
> to resolve them. And perhaps other will fail because the DBMS knows
> several ways to translate the assignment but it can not decide which
> to apply.
>
> In case we can't know any of the translations we could return a value
> instead of a variable, but this is a choice for the implementors.
>
>>Therefore updatability of views cannot be viewed as a general mechanism >>in the model but rather as a synctactic shorthand that deals with >>special cases by translating them to real updates of real tables.
>
> Non sequitur. Of course views are not a syntactic shorthand.
What if they are syntactic shorthands - as long as it is clearly defined what they are shorthands for, I don't see a problem?
> I would like to know what the other comp.databases.theory folks think
> about all this.
Received on Fri Sep 24 2004 - 13:39:08 CEST