Re: view updates (was something else)
Date: Sat, 04 Nov 2006 02:18:21 GMT
Message-ID: <NLS2h.248014$1T2.171272_at_pd7urf2no>
Aloha Kakuikanu wrote:
> paul c wrote:
>> Aloha Kakuikanu wrote:
>>> NENASHI, Tegiri wrote:
>>>> Jan Hidders wrote:
>>>>> Do you know of any results that might be interesting for database
>>>>> theory and could not already be shown with good old set theory?
>>>> The categorical sketches to use for universal view updatability:
>>>>
>>>> Michael Johnson and Robert Rosebrugh.
>>>> Universal view updatability
>>> They claim to solve view updatability? OK, I have a table RealPeople
>>> with one attribute Name and the view
>>>
>>> CDTPosters =
>>> RealPeople
>>> union
>>> {(name=TeGiriNeNashi)}
>>>
>>> and a constraint
>>>
>>> RealPeople
>>> intersect
>>> {(name=TeGiriNeNashi)}
>>> =
>>> {}
>>>
>>> Is the CDTPosters view updatable?
>> I like that example, but can you come up with one that doesn't involve a
>> constraint? (I think constraints muddy the waters and at worst confuse
>> us with un-related questions.)
>
> I would argue that constrants clarify the picture. Without this
> constraint when adding the record {(name=TeGiriNeNashi)} into the
> CDTPosters view we have ambiguity. ...
What is the ambiguity? Because of the name, I assume RealPeople is a 'real' relation. I think one must look at the real relation that receives the insert. In this case, there seems to be only one. I would like to see an example with two. In that case, my question would still be what is the ambiguity, ie., is the result of the 'or'/'union' still true? If it is, then I don't see any ambiguity as far as the viewer is concerned. Whether some implementation wants to arbitrarily forbid such an operation is a question for the implementer.
p Received on Sat Nov 04 2006 - 03:18:21 CET