system/classes/Model.php
protected function _isRelation($attributeName) 
    {
      // Grab attribute definition
      $def = $this->model_attributes[$attributeName];
      return isset($def['models']) || isset($def['model']);
    }
protected function _isRelation($attributeName) 
    {
      // Grab attribute definition
      $def = $this->model_attributes[$attributeName];
      return isset($def['models']) || isset($def['model']);
    }
Returns true or false depending on if the attribute specified is a relation to another model(s) or not.

@return bool