Board Representation (chess) - Requirements

Requirements

A full description of a chess position, i.e. the position "state", should contain the following elements:

• The location of each piece on the board
• Whose turn it is to move
• Status of the 50-move draw rule. The name of this is sometimes a bit confusing, as it is 50 moves by each player, and therefore 100 half-moves, or ply. For example, if the previous 80 half-moves passed without a capture or a pawn move, the fifty-move rule will kick in after another twenty half-moves.
• Whether either player is permanently disqualified to castle, both kingside and queenside.
• If an en passant capture is possible.

Board representation typically does not include the status of the threefold repetition draw rule. To determine this rule, a complete history of the game from the last irreversible action (capture, pawn movement, or castling) needs to be maintained, and so, is generally tracked in separate data structures.