View Updates Problem Statement

> "Bob Badour" <bbadour_at_golden.net> wrote in message
> news:Vd97b.717$zB.69216404_at_mantis.golden.net...
> > Suppose we extend the syntax for view definition to allow systematic
> default
> > values:
> >
> > view A as
> > select a from X
> > default X set b = 0 on insert to A

Here is alternative suggestion:

Given a set of views

V1, V2, ... VN

and a set of insert/delete operations upon those views, for example

insert ('John', 20) into V1
delete from V2 where name = 'Mary'
...

translate those view updates into the base relations.

Comments.
1. We need to consider more than one view in order to be able solve ambiguous cases.
2. It is not clear if artificially combining views like in the example of union&symmetric difference is a good idea. 3. Constraints are views that evaluate to constants. For example, if we define

view V3
select max(sal) from (

    select sal from emp
    union
    select 1000 from DEE
)

then constraint "each emp has salary no more than 1000" can algebraically be written as

V3*x = 1000

where "V3*x" means view V3 applied to a set of base relations x, and "1000" means an output relation that has one tuple with a single value 1000. Received on Tue Sep 09 2003 - 02:45:19 CEST