Re: Jan's well-defined view updates definition

Mikito Harakiri wrote:
>
> We can't continue going round and round, so let's move on to the second
> paragraph of your definition.

Well, I would still be interested in your opinion on whether the definition I gave makes sense or not, and what the intuition is behind the definitions you gave. It's almost as if you are affraid of such discussions.

> "Jan Hidders" <jan.hidders_at_pandora.be> wrote:
>> Finally, we define a view V as *updatable* by a certain set of updates U
> if
>> for all databases D that satisfy the schema all updates in U are
>> well-defined. Additionally we say that V is *commutatively updatable* by
>> U if for all databases D that satisfy the schema it holds that if two
>> series of updates from U have the same result when applied to Q(V) and
>> perform only well-defined updates then they result in the same database
>> when applied to D.
>
> Could you please provide a non-commutatively updatable example that we can
> discuss?

Lets say I have base relations R(a,b) and S(b,c) with a foreign key R.b -> S.b and a view V that is defined by the natural join of R and S. The additions and deletions are both well-defined but if I add the tuple (a1,b1,c1) and then remove it then the end result is an additional tuple (b1,c1) in S, which is not the same as the end result of adding 0 tuples. So for the class of updates that consists of inserts and deletes it is not commutatively updatable.

• Jan Hidders