This is my UML Class Diagram made in Astah Community, for a tennis scoreboard game.

Here's a link to the image (I don't have enough rep to post images): http://i47.tinypic.com/2lsxx90.png

• Points are calculated based on moves.
• Moves can be either points (for the player's advantage) or errors (for the opponent's advantage).
• The Time Machine allows you to travel to previous game states (expressed as scoreboards).
• The storage component should be able to store matches independently of the serialization format.
• The serializers and deserializers should be able to do their job regardless of where the storage lies.
• The GameEngine should be able to apply the rules of the game regardless of the particularities of the game (hence, dependency injection through the Settings class).
• The outcomes of games, sets and matches should be deducible based on the points and the rules to apply (the logic implementations are there to provide the rules).

Could you please verify my design and tell me if there's anything wrong with it? Thanks in advance.