Re: Multiple keys and transition constraints
From: J M Davitt <jdavitt_at_aeneas.net>
Date: Fri, 15 Sep 2006 12:45:46 GMT
Message-ID: <_fxOg.57$8e5.34_at_tornado.ohiordc.rr.com>
>>Brian Selzer wrote:
>>
>>>"JOG" <jog_at_cs.nott.ac.uk> wrote in message
>>>news:1158251660.983027.98520_at_e3g2000cwe.googlegroups.com...
>>>
>>>
>>>>Brian Selzer wrote:
>>>>
>>>>
>>>>>Given a relation schema R {A, B, C}, where A and B are each candidate
>>>>>keys.
>>>>>
>>>>>If the current extension is
>>>>>
>>>>>r {{A:1, B:9, C:3}
>>>>> {A:2, B:8, C:4}}
>>>>>
>>>>>and the proposed extension is
>>>>>
>>>>>r' {{A:1, B:8, C:4}
>>>>> {A:2, B:9, C:3}}
>>>>>
>>>>>is only A different? Or are both B and C different? From one
>>>>>perspective,
>>>>>both B and C remain constant but A is different. From another
>>>>>perspective,
>>>>>A remains constant but both B and C are different. If you're trying to
>>>>>specify the allowable transitions for C, which key do you use? A, B,
>>>>>the
>>>>>superkey, AB, or none of the above?
>>>>
>>>>This requires more information to answer.
>>>>
>>>>Can you tell us which attribute identifies the subject [of each
>>>>proposition] in real life over the updates. Then I can determine /what/
>>>>exactly has experienced the transition.
>>>>
>>>>No other questions, just that.
>>>>
>>>
>>>
>>>Well, that's the dilemma, there are two subjects because there are two
>>>keys. Consider the following relation:
>>
>>[Why do you flog yourself with this nonsense?!]
>>
>>"subjects." "keys." Hmm... re: r v. r':
>>
>>B is a key, you say? Well, the same determinant
>>values in B have different dependent values. So?
>>
>>A is a key, you say? Well, the same determinant
>>values in A have different dependent values. So?
>>
>>If that design doesn't make you happy, concoct
>>one that will.
Date: Fri, 15 Sep 2006 12:45:46 GMT
Message-ID: <_fxOg.57$8e5.34_at_tornado.ohiordc.rr.com>
Brian Selzer wrote:
> "J M Davitt" <jdavitt_at_aeneas.net> wrote in message > news:N_oOg.42$8e5.29_at_tornado.ohiordc.rr.com... >
>>Brian Selzer wrote:
>>
>>>"JOG" <jog_at_cs.nott.ac.uk> wrote in message
>>>news:1158251660.983027.98520_at_e3g2000cwe.googlegroups.com...
>>>
>>>
>>>>Brian Selzer wrote:
>>>>
>>>>
>>>>>Given a relation schema R {A, B, C}, where A and B are each candidate
>>>>>keys.
>>>>>
>>>>>If the current extension is
>>>>>
>>>>>r {{A:1, B:9, C:3}
>>>>> {A:2, B:8, C:4}}
>>>>>
>>>>>and the proposed extension is
>>>>>
>>>>>r' {{A:1, B:8, C:4}
>>>>> {A:2, B:9, C:3}}
>>>>>
>>>>>is only A different? Or are both B and C different? From one
>>>>>perspective,
>>>>>both B and C remain constant but A is different. From another
>>>>>perspective,
>>>>>A remains constant but both B and C are different. If you're trying to
>>>>>specify the allowable transitions for C, which key do you use? A, B,
>>>>>the
>>>>>superkey, AB, or none of the above?
>>>>
>>>>This requires more information to answer.
>>>>
>>>>Can you tell us which attribute identifies the subject [of each
>>>>proposition] in real life over the updates. Then I can determine /what/
>>>>exactly has experienced the transition.
>>>>
>>>>No other questions, just that.
>>>>
>>>
>>>
>>>Well, that's the dilemma, there are two subjects because there are two
>>>keys. Consider the following relation:
>>
>>[Why do you flog yourself with this nonsense?!]
>>
>>"subjects." "keys." Hmm... re: r v. r':
>>
>>B is a key, you say? Well, the same determinant
>>values in B have different dependent values. So?
>>
>>A is a key, you say? Well, the same determinant
>>values in A have different dependent values. So?
>>
>>If that design doesn't make you happy, concoct
>>one that will.
> > > I am completely at a loss as to the content and purpose of your post: What > nonsense? Are you questioning whether A and B are keys? Are you saying > that transition constraints are irrelevant? What is your point? Mind > reading isn't my forte, so could you please be a little more specific?
Just like that "replacement v. modification" issue you raised. Received on Fri Sep 15 2006 - 14:45:46 CEST