Re: teaching relational basics to people, questions

From: Mr. Scott <do_not_reply_at_noone.com>
Date: Mon, 14 Dec 2009 19:39:15 -0500
Message-ID: <YoCdnQvhRIa3RrvWnZ2dnUVZ_hCdnZ2d_at_giganews.com>


<compdb_at_hotmail.com> wrote in message news:f8fb0e4b-100a-4466-b968-5099852ecaa4_at_2g2000prl.googlegroups.com...
> On Dec 11, 1:29 pm, Kevin Kirkpatrick <kvnkrkpt..._at_gmail.com> wrote:
>> Hello Mr. Scott,
>> If I'm understanding your explanation properly, in a database with
>> only table:
>> BIG_US_CITIES {CITY_NAME, STATE_CODE}
>> (that is, lacking table STATES {STATE_CODE}) one must logically infer,
>> from the CWA, that states with no big cities, e.g. 'RI', do not exist?
>
> On Dec 11, 1:36 pm, Gene Wirchenko <ge..._at_ocis.net> wrote:
>> Effectively yes.
>
> On Dec 11, 8:15 pm, "Mr. Scott" <do_not_re..._at_noone.com> wrote:
>> There isn't anywhere to record the assertion that there is a
>> state with no big cities, so there can't be any.
>
> It is more reasonable to say that the database is silent about the
> existence of states and cities. But even if it did, the inference that
> some state doesn't exist is wrong.

No, it isn't wrong. An assertion that there is a state with no big cities is inconsistent with the definition of the database: it cannot be true.

<snip> Received on Mon Dec 14 2009 - 18:39:15 CST

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