Re: Little design mistakes that can be easily avoided (2): Listenning to CELKO (and CELKO alikes)
From: Brian Selzer <brian_at_selzer-software.com>
Date: Tue, 29 May 2007 11:48:42 GMT
Message-ID: <uqU6i.12476$RX.10059_at_newssvr11.news.prodigy.net>
>> "Gene Wirchenko" <g..._at_ocis.net> wrote in message
>>
>> news:cc0m53lkdf0os673kfdunubc46dkidq1uo_at_4ax.com...
>>
>> > Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote:
>>
>> > [snip]
>>
>> >>It is /always/ a superkey. It might be "candidate" (i.e. irreducible)
>> >>as
>> >>well; if not, it is a /proper superkey/. (Also, a tuple is not a key,
>> >>but I'll quibble about that some other time:)
>>
>> > Why can't a tuple be a key? It does uniquely specify a tuple.
>>
>> Because a tuple is a value and a key is a constraint.
> How do you isolate a single tuple ?
>
>> > Sincerely,
>>
>> > Gene Wirchenko
>>
>> > Computerese Irregular Verb Conjugation:
>> > I have preferences.
>> > You have biases.
>> > He/She has prejudices.
>
> Received on Tue May 29 2007 - 13:48:42 CEST
Date: Tue, 29 May 2007 11:48:42 GMT
Message-ID: <uqU6i.12476$RX.10059_at_newssvr11.news.prodigy.net>
"Cimode" <cimode_at_hotmail.com> wrote in message news:1180428899.661996.130960_at_w5g2000hsg.googlegroups.com...
[Quoted] > On May 28, 9:16 pm, "Brian Selzer" <b..._at_selzer-software.com> wrote:
>> "Gene Wirchenko" <g..._at_ocis.net> wrote in message
>>
>> news:cc0m53lkdf0os673kfdunubc46dkidq1uo_at_4ax.com...
>>
>> > Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote:
>>
>> > [snip]
>>
>> >>It is /always/ a superkey. It might be "candidate" (i.e. irreducible)
>> >>as
>> >>well; if not, it is a /proper superkey/. (Also, a tuple is not a key,
>> >>but I'll quibble about that some other time:)
>>
>> > Why can't a tuple be a key? It does uniquely specify a tuple.
>>
>> Because a tuple is a value and a key is a constraint.
> How do you isolate a single tuple ?
>
{t | exists t in r and t[K] = k}
K is a set of *names*, k is a set of named *values*.
key: forall r |r| < 2 or (|r[K]| = |r| and not exist x in K |r[K - x]| = |r|)
>
>> > Sincerely,
>>
>> > Gene Wirchenko
>>
>> > Computerese Irregular Verb Conjugation:
>> > I have preferences.
>> > You have biases.
>> > He/She has prejudices.
>
> Received on Tue May 29 2007 - 13:48:42 CEST