I'm building a program registration system that will have a complex data structure. There are programs (custom post type, CPT), teachers (CPT), registrations (custom table and meta table), payments (custom table and meta table), and later accommodations (CPT) and lastly Users (wp users table).
I want to be able to use nice wordpress taxonomy features with my custom registration and payment tables. But I'm assuming I can't because the taxonomy system is only for the posts table. Is this correct? Basically I want to easily assign categories to registrations, and later be able to search on that, and have it flexible so the user can create their own categories.
I ruled out using custom post type for the registrations and the payment tables only because then I would need a separate plugin to link everything up (scribu's post to post plugin) and it would make any mysql queries incredibly complicated.
any advice would be greatly appreciated.