@@ -9,8 +9,13 @@ public class Constants {
   public static final String ATTEMPTS_KEY = "attempts";
   public static final String ID_KEY = "id";
 
+  public static final String FLOW_ID_KEY = "flowId";
+  public static final String FLOW_VERSION_KEY = "flowVersion";
+  public static final String EXPERIMENT_ID_KEY = "experimentId";
+
 
 
   public static final String DEFAULT_500_ERROR_MESSAGE = "Unexpected error encountered.";
+  public static final String DEFAULT_404_ERROR_MESSAGE = "The requested resource was not found.";
 
 }
package cloudflow.servlets;

public class Constants {

  public static final String EXECUTION_ID_KEY = "execution_id";
  public static final String START_TIME_KEY = "start_time";
  public static final String END_TIME_KEY = "end_time";
  public static final String STATUS_KEY = "status";
  public static final String ATTEMPTS_KEY = "attempts";
  public static final String ID_KEY = "id";



  public static final String DEFAULT_500_ERROR_MESSAGE = "Unexpected error encountered.";

}

Nit: Not part of your change, it would be nice to add "server" in the message so it is clear to users who are not familiar with HTTP error codes.