title: Where to place "common" classes in YII Framework structure?
body: <p>I need to create a few classes and would like some help on where this would go in the YII Framework. I know if I create a Model, it must go in the "models" directory. And by the same logic I know where "views", "controllers" etc would go. However, where would the following be placed in my web application:</p>
  
  <ol>
  <li>A class that contains a variety of "number" functions such as currency conversion, metric conversions etc?</li>
  <li>A class that interacts with a REST API? (It interacts with the database)</li>
  </ol>
  
  <p>Any tips?</p>