Re: database integrity

"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:K%6je.95748$hi2.5651565_at_phobos.telenet-ops.be...
> Kenneth Downs wrote:
>>
>> One question on my mind is the change in rules over time. Do we say:
>>
>> 1. Data is valid if it adheres to all existing biz rules, OR:
>> 2. Data is valid if it adheres to rules that were in force when it was
>> inserted or updated.
>
> Very interesting question. I would say that it is the simplest to let the
> static database constraints be applicable for all the data, and if you
> want to restrict what can be added (or deleted or updated) then you use
> dynamic database constraints (or transition constraints, as they are also
> called) to specify that.

Additionally, in more complex change, the retrospectively entered data may need to be addressed and essentially "converted" to conform to the implementation of new rules. This conversion will be a once off update of the data, to get it to conform to new rules.

In this sense, the second option above, is false: ie - data may not be valid because the rules have changed.

The first answer seems to be the only viable answer. Also, to test the integrity of the data, the exception checking can make use of the negative of that statement ...

1. Data is invalid if it does not conform to current biz rules.

> I've always wondered why this is never mentioned as an example of the
> usefulness of dynamic database constraints.

Mentioned by whom?

Pete Brown
Falls Creek
Oz
www.mountainman.com.au Received on Sat May 21 2005 - 08:33:21 CEST