  Game extension is an entertaining activity that offers an opportunity to test
new design approaches by non-programmers. The real challenge is to enable this
activity by means of a suitable infrastructure. We propose a knowledge-driven
approach with natural game-player concepts. These concepts, found in game
ontologies, include game abstractions and rules for game moves. The approach
has been implemented and tested for board games. These include tic-tac-toe as a
simplest example, enabling extensions of tic-tac- toe, say to a four-by-four
board and Sudoku, a single player game of a very different nature.
