Re: Serial, concurrent, parallel

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?