Database Schema

I know WordPress is a proven product and the developers know a lot more about programming than I do, so I don’t want this to seem like a rude question, I’m just trying to learn about how it works.

I noticed that the database isn’t really in 3NF. Things like categories and tags are combined into a single table instead of a table called Categories and Tags and the settings are all stored in an options table with fields like option name and option value that don’t really describe what data they contain.

Anyway, most of the database is like this and I’m wondering if there is any performance value for doing it that way, or why it’s done that way. I know it has to work considering the number of large websites that seem to run on WordPress without any problems.

I want to make some plugins and themes, so I’m trying to wrap my head around the database. Is it a normal design, or is there something unique going on? I’ve been looking through the documentation to see what everything does, but it doesn’t really explain the reasons for the chosen design/schema.