How Are Categories Added?

I’m writing a seperate script that needs to be able to add a new category into my blog.

The only place where I found the info is stored is in wp_categories in the database, and I’ve made it add the categories there.

That works, except under Permalinks.
Then, it gives me a 404 error. But if I go in and edit the category but don’t even change anything, it works.

Am I missing another table that I should modify?

Thanks