When is taxonomy appropriate If I, hypothetically, ran a business and kept data on products, part data related to those products, and service procedures for those products would it make sense to fit this into the Drupal taxonomy? Is that the Drupal way?

I'm just getting going on Drupal; I have an existing working php application that I shoved into a module without really making use of Drupal functions, to the extent that I even have a separate database. My app uses some non-trivial database organizations, lots of database views and heavy usage of inner joins. This app will be a suite of apps that will also include standard web functions, which I why I want to use Drupal/CMS. But I don't know if I should my module data into taxonomies.

Edit: 99% sure that entities will do what I need, searching on that now.
Taxonomies are best used to define properties that:


are shared across multiple content items;
need to be grouped with similar properties.


For instance, if you're selling t-shirts, the taxonomy terms 'blue', 'red' and 'yellow' are grouped in the 'color' vocabulary. By tagging all t-shirts of the same color with the same taxonomy term, you define a relationship between those t-shirts. This makes it very easy to generate a page showing all blue, red or yellow t-shirts.

Taxonomy terms, like many other entity types, are 'fieldable', which means that you can add fields to them to contain data. For instance, if you add an image field to the taxonomy terms in the 'color' vocabulary, you could define an example image for each color term.

If this example with t-shirts and colors matches your use case, then the answer to your question is: Yes, taxonomy is the Drupal way to do it.

By the way, the word "entity" has a very broad meaning in Drupal. 'Taxonomy term' is a type of entity, just like 'node', 'user' and 'file'. Saying that "entities will do what you need" is like saying "building materials will allow me to build a house". It's a statement that (almost) can't be wrong. You need to answer the question: Which type of entity is best to solve this specific problem?