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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Serial, concurrent, parallel
Date: Fri, 17 Jan 2025 14:08:53 -0700
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On 1/17/2025 1:50 PM, Don Y wrote:
> E.g., my Cities table lists all of the names of the cities
> found in any state/territory in the US.  The States table
> just lists the names of states/territories.  Entirely different
> lengths and meanings to the data.  The Localities table
> contains pairs of (city, state) identifiers (the identifiers
> defined and mapped to specific cities/states by those
> respective tables).
> 
> You can TRY to build a spreadsheet that LOOKS like this.
> But, it won't GUARANTEE that the identifiers for the city
> (and state) defined for "locality 1" are valid city (and
> state) identifiers.  This doesn't just apply to entering
> the data but, also, modifying it and deleting it!
> 
> E.g., if you try to *delete* the city "Chicago" from the
> city table, the database won't let you -- because there
> is a locality that references it:  (ChicagoID, IllinoisID)

The DBMS will *guarantee* (if the scheme so declares) that
no two cities (or states) have the same NAME *or* identifier.
It will also insist that every name *has* an identifier.

So, you can't have two Alaskas defined -- with different
identifiers.  Or, two Chicagos.

How are you going to do that in a spreadsheet?