Causal Normalization: A Methodology for Coherent Story Logic Design in Computer Role-Playing Games

Abstract

A common experience in playing computer role-playing games, adventure games, and action games is to move through a complex environment only to discover that a quest cannot be completed, a barrier cannot be passed, or a goal cannot be achieved without reloading an earlier game state and trying different paths through the story. This is typically an unanticipated side effect caused by the player having moved through a sequence of actions or a pathway different from that anticipated by the game designers. Analogous side effects can be observed in traditional software engineering (referred to as data coupling and control coupling), in database design (in terms of unnormalized relations), and in knowledge base design (in terms of unnormalized truth-functional dependencies between declarative rules). In all cases, good design is a matter of minimizing functional dependencies, and therefore coupling relationships between different parts of the system structures, and deriving system design from the minimized dependency relationships. We propose a story logic design methodology, referred to as causal normalization, that minimizes some forms of causal functional dependency within story logics and therefore eliminates some unintended forms of causal coupling. This can reduce the kind of unexpected dead ends in game-play that lead to player perceptions of poor game design. Normalization may not be enough, however. Extending the principle of minimal coupling, we propose an object-oriented approach to story logic, and relate this to principles of normalization and game architecture.