Re: view update in logic and relational databases

paul c wrote:

>Sampo Syreeni wrote:
>> Like most people around here, I periodically return to the view update
>> problem. I also subscribe to the idea that relational databases are
>> fundamentally about predicate logic, and that a proper interpretation
>> of the update problem probably has to be explained in logic terms. So
>> I'd like to offer one purely logical solution to the problem.

This has been studied extensively ...

[...]

>I think a more important question is whether a 'relational logic' that
>deals with views as well as it deals with base variables is somehow
>inconsistent or leads to contradictory conclusions.

Another is performance - answering queries must be feasible.

>Such a logic might
>not be comparable with traditional logic, but I'd say consistency is the
>more important quality for interpretation and optimization. I think it
>is most important to ask what a particular choice of logic buys us and
>what it doesn't, even if that might lead to a distortion of predicate
>logic.

It doesn't, but you have to go beyond predicate logic because it isn't powerful enough.

See e.g.

  http://infolab.stanford.edu/~ullman/cs345-notes.html

(not that I have read all of those)

-- 
Reinier