internal static void Activate()
        {
            if (!DesignerProperties.IsInDesignTool)
            {
                _engine = new SterlingEngine();
                try
                {
                    // engine could be already activated (in main application or some referenced dll);
                    _engine.Activate();
                }
                catch (SterlingActivationException ex)
                {
                }

                _driver = new IsolatedStorageDriver("EPubReader/");

                try
                {
                    _database = _engine.SterlingDatabase.GetDatabase("EPubReader Database");
                }
                catch (SterlingDatabaseNotFoundException ex)
                {
                    _database = _engine.SterlingDatabase.RegisterDatabase <Database>(_driver);
                }
            }
        }
        internal static void Deactivate()
        {
            if (_engine != null)
            {
                _engine.Dispose();
            }

            _engine   = null;
            _driver   = null;
            _database = null;
        }