Taxonomy Parent-Child relationships => storing foreign keys instead of text in fields

Going through the Drupal documentation on "Organising content with taxonomies", one of the guidelines is to divide up vocabularies when parent-child relationships are required and the number of terms is high.
In a properly designed database environment, tables are joined by "foreign keys". If I use the table analogy with vocabularies, I would like to know if this works (or can work) the same way. Let me try to explain.

First use case:

Imagine a user profile page, in which a user can select a motorcycle brand via a term reference field linked to a vocabulary storing all available brands. This vocabulary has the brand listed in its description, while a field is added to store an integer, that acts as a unique "foreign key".

What I want:

when the user selects the brand in the user profile page, the brand name should be visible in the field, but I would like its underlying field (on the user profile page) to store the "key", and not the text in the description.

Benefits:

if for whatever reason I need to change the description/brand name, the user profile for all users with the same motorcycle brand will automatically show the change.

Second use case:

A first vocabulary stores all kind of motorcycle brands. This vocabulary has the brand listed in the description, while a field is added to store an integer, that acts as an unique "foreign key".
A second vocabulary stores only motorcycle types, a field that acts as the unique key for the type, while a second field stores a link to the corresponding brand.

What I want:

to use the unique brand key, as a "foreign key" to reference/link to the brand name in the motorcycle type vocabulary.

Benefits:

a) I am not storing dozens of the same motor brand in text form in the motor type vocabulary, b) if for whatever reason I need to change the brand name description (in the brand vocabulary), I do not have to update the motor type vocabulary, c) by selecting the motor type in any kind of content type, I have automatically access to the brand that is linked to it.

Right now I have played around establishing a parent-child relationship by using a term reference field. But that only allows me to store the description text, not the "key". There is no way (as I see it) to do what I describe above. And frankly, this to me defeats the purpose of parent-child relationships altogether. So I guess I must be missing something.... and could use some help from the community.

Just to be clear, I am a fairly new Drupal site developer, a hobbyist, have done lots and lots of reading & searching on internet about Drupal (including on this topic). Working on my very first web site for a couple of months now, but I am by no means a coder (although willing to learn). As such I am lacking a full overview on Drupal's capabilities (if that is at all possible...). Any pointers into the right direction would be extremely helpful.