Hello, I think you should do it as logical and as similar to the real life as possible. IN the real life, the player knows only where he is In a player perspective, if he want to get informations about other players, he should ask his environment. IN this case, the field. In its side, a field should know who are on it, to be able to give information to the players. You have a bidirectionnal association. One side of the association may be useless, depending on the situation, it's impossible to tell you without a more precise example. It depends on what a player can do with the field, and what the field can do with the players. IN the football example, the field would probably be just a container which can only let players enter and exit and allow to iterate through the players who are in game.