Luis Valente,  Aura Conci,  Bruno Feijó. 

Computer games can be regarded as state machines as far as their stages are concerned. The traditional design for this state machine is to assign ids to the states and to use conditional constructs to direct the game execution to the proper state. However, this approach is not robust enough and can quickly get out of control. This work proposes an object-oriented model to state specification and management, which features state hierarchies.

http://www.lbd.dcc.ufmg.br/colecoes/sbgames/2006/003.pdf

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