title: Proper way to handle Model constants in Magento
body: <p>What is the proper way to handle constants in models with Magento?
  For example, I have an <code>Export</code> class that have numerous status', such as </p>
  
  <ul>
  <li>Cancelled</li>
  <li>Pending</li>
  <li>Failed</li>
  <li>Complete</li>
  </ul>
  
  <p>Currently, I have these defined at the top of the model like this, but I feel this is not the best solution:</p>
  
  <pre><code>  define("CANCELLED","Cancelled");
    define("INCOMPLETE","Incomplete");      
    define("PENDING","Pending");
    define("COMPLETE", "Complete");
  </code></pre>
  
  <p>For instance, in a controller, if I want to update the status of a sales order (which has custom fields that my model references) with PENDING, at the moment, I am running the below purely so that it includes the file that has the constants defined:</p>
  
  <pre><code>Mage::getModel("efinterface/export");
  </code></pre>
  
  <p>Any advice appreciated.</p>