I have done research on the different kinds of architectures but I'm still not too comfortable choosing between 3-tier and 4-tier.
What constitutes a 4-tier system?
My application is as follows:
The client is based on iOS iPhone app using MVC pattern.
The server is based on Ruby on Rails using MVC pattern as well. (certain views are rendered in HTML if requests don't come from iPhone)
The database is MySQL accessed by MySQL2 Gem.
The client and the server both access web services from Google's API and other webservices.
What is my system's architecture?