Re: Multiple keys and transition constraints
From: Brian Selzer <brian_at_selzer-software.com>
Date: Fri, 15 Sep 2006 04:07:56 GMT
Message-ID: <wGpOg.1139$vJ2.150_at_newssvr12.news.prodigy.com>
>> "JOG" <jog_at_cs.nott.ac.uk> wrote in message
>> news:1158251660.983027.98520_at_e3g2000cwe.googlegroups.com...
>>
>>>Brian Selzer wrote:
>>>
>>>>Given a relation schema R {A, B, C}, where A and B are each candidate
>>>>keys.
>>>>
>>>>If the current extension is
>>>>
>>>>r {{A:1, B:9, C:3}
>>>> {A:2, B:8, C:4}}
>>>>
>>>>and the proposed extension is
>>>>
>>>>r' {{A:1, B:8, C:4}
>>>> {A:2, B:9, C:3}}
>>>>
>>>>is only A different? Or are both B and C different? From one
>>>>perspective,
>>>>both B and C remain constant but A is different. From another
>>>>perspective,
>>>>A remains constant but both B and C are different. If you're trying to
>>>>specify the allowable transitions for C, which key do you use? A, B,
>>>>the
>>>>superkey, AB, or none of the above?
>>>
>>>This requires more information to answer.
>>>
>>>Can you tell us which attribute identifies the subject [of each
>>>proposition] in real life over the updates. Then I can determine /what/
>>>exactly has experienced the transition.
>>>
>>>No other questions, just that.
>>>
>>
>>
>> Well, that's the dilemma, there are two subjects because there are two
>> keys. Consider the following relation:
Date: Fri, 15 Sep 2006 04:07:56 GMT
Message-ID: <wGpOg.1139$vJ2.150_at_newssvr12.news.prodigy.com>
"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? Received on Fri Sep 15 2006 - 06:07:56 CEST