Re: Updatable views

>> My question was and is: can somebody prove that this can't be done in
>> general or can't be done in certain circumstances ?

There may not be full fledged conclusive theoretical work available on this regard. Some related work by Stephen Hegner and Arthur Keller can be found online. McGoveran's guidelines on view updates can be found at the dbdebunk site.
http://www.dbdebunk.com/page/page/1396086.htm

With SQL, it is mostly adhoc. You can conclude view updates in SQL can be done only in rare circumstances for two main reasons: (1) SQL does not support closure and (2) A view definition in SQL is not a true projection. As a result product manuals generally have a huge set of restrictions detailed regarding their view updateability provisions.

-- 
Anith