Re: teaching relational basics to people, questions

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

<> wrote in message
> On Dec 11, 1:29 pm, Kevin Kirkpatrick <> wrote:
>> Hello Mr. Scott,
>> If I'm understanding your explanation properly, in a database with
>> only table:
>> (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 <> wrote:
>> Effectively yes.
> On Dec 11, 8:15 pm, "Mr. Scott" <> 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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