Re: On view updating

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sat, 25 Sep 2004 14:00:57 +0200
Message-ID: <41555dfa$0$78279$e4fe514c_at_news.xs4all.nl>

Paul wrote:

> Paul wrote:
>

>>> Sure very simple. Try to let the user input the known fact that
>>> X=2 OR X=3. Say "mary has blue eyes or mary has green eyes".
>>>
>>> Or to say that "Whoever has blue eyes will be likable to john"
>>
>>
>> These are just constraints though, which a database can handle. It's 
>> just that users restricted to DML can't specify it.

>
>
> just thought about this some more, and I realise now that the database
> can only contain these constraints "X=2 OR X=3" if one or the other of
> the statements is explicitly contained within the database. Because
> anything not in the database is assumed to be false.

Nice. "Grote stappen gauw thuis." (Dutch saying, meaning something like "Big steps bring you home fast.") Sometimes you have to consider the details. Constraints are statements about what may be in the database, and yes they can be expressed in the database.

The interpretation of "X=2 OR X=3" as a constraint is: Every assertion containing a value for X should have 2 or 3 as the value for X. It specifically does not assert that there should be assertions containing a value for X.

If there is no assertion having a value for X, the constraint is not violated. Received on Sat Sep 25 2004 - 14:00:57 CEST