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The Cooperative Contract 233To support this mediation we are developing a system that sits behind thescenes of a computer game engine, directing the unfolding action while monitoringand reacting to all user activity. The system, called Mimesis[6], uses thefollowing components:1. A declarative representation for action within the environment. This mayappear in the type of annotations to virtual worlds suggested by Doyle andHayes-Roth [4], specifically targeted at the representational level required topiece together plot using plan-based techniques described below.2. A program that can use this representation to create, modify and maintaina narrative plan, a description of a narrative-structured action sequence thatdefines all the activity within the game. The narrative plan represents the activitiesof users, system-controlled agents and the environment itself. This programconsists of two parts: an AI planning algorithm such as Longbow [7] and anexecution-management component. The planning algorithm constructs plansfor user and system interaction that contain such interesting and compellingnarrative structure as rising action, balanced conflict between protagonist andantagonist, suspense and foreshadowing. The execution manager issues directivesfor action to the system’s own resources (e.g., the story’s system-controlledcharacters), detects user activities that deviate from the planned narrative andmakes real-time decisions about the appropriate system response to such deviations.The response might take the form of re-planning the narrative bymodifying the as-yet-unexperienced portions of the narrative plan, or it mighttake the form of system intervention in the virtual world by preventing the user’sdeviation from the current plan structure.3. A theory capable of characterizing plans based on their narrative aspects.This theory informs the program, guiding the construction of plans whose localand global structure are mapped into the narrative structures of conflict,suspense, etc.4. ConclusionsPeople interact with systems such as computer games by using many ofthe same social and communicative conventions that are seen in interactionsbetween people [8]. I propose that expectations about collaboration betweencomputer game players and game systems (or their designers) that licenses boththe game players’ and the game designers’ understanding of what components ofthe game mean. Consequently, the co-operative nature of the gaming experiencesets expectations for the behavior of both the game and its players. As computerand console games become more story-oriented and interactivity within thesegames becomes more sophisticated, this co-operative contract between gameand user will become even more central to the enjoyment of a game experience.