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Re: database design method

From: Lauri Pietarinen <lauri.pietarinen_at_atbusiness.com>
Date: Mon, 18 Nov 2002 09:35:45 +0200
Message-ID: <3DD89851.71B3CCFC@atbusiness.com>


Jan,

thanks for the trouble for trying to clarify.

There must be some underlying assumptions that I juat don't understand, because I fail to follow your argumentation.

The only question I know how to ask is the following:

>>> Suppose I have a relation
>>>
>>> Bought(customer, product)
>>>
>>> and I want as the result a relation
>>>
>>> Cust_class(class_id, customer)
>>>
>>> that groups the customers into classes that have bought the same set of
>>> prodcucts and gives them a new identifier.

> > - I would suppose that the id's could be generated
> >each time the query was executed - what's the problem?
>
> If it is executed a lot you may run out of them.

Surely if that same view (that generates - perhaps abstract - identifiers) is queried many times, it represents each time the values of the execution at that point of time. So if I query it twice it makes no difference whether the identifiers are the same or not, or what the result of the query is.

So if I say

 select * from cust_class

     and get the answer {(1,1),(1,2),(2,3)}

and re-execute it after 10 minutes

   and get the answer {(1,1),(2,2),(2,3)}

that would be perfectly correct because
it would just be the result of the query and that's it.

regards,
Lauri Pietarinen Received on Mon Nov 18 2002 - 01:35:45 CST

Original text of this message

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