U-director: a decision-theoretic narrative planning architecture for storytelling environments

Recent years have seen significant growth in work on interactive storytelling environments. A key challenge posed by these environments is narrative planning, in which a director agent orchestrates all of the events in a storyworld to create an optimal experience for a user, who is herself an active participant in the unfolding story. To create effective stories, the director agent must cope with the task's inherent uncertainty, including uncertainty about the user's intentions and the absence of a complete theory of narrative. Director agents must be efficient so they can operate in real time. In this paper, we present U-Director, a decision-theoretic narrative planning architecture that dynamically models narrative objectives (e.g., plot progress, narrative flow), storyworld state (e.g., plot focus), and user state (e.g., goals, beliefs) with a dynamic decision network that continually selects storyworld actions to maximize narrative utility on an ongoing basis. The U-DIRECTOR architecture has been implemented in a narrative planner for Crystal Island, an interactive storyworld in which users play the role of a medical detective solving a science mystery. Preliminary evaluations suggest that the U-DIRECTOR architecture satisfies the real-time constraints of interactive environments and creates engaging narrative experiences.