Modeling Games with Petri Nets

Key insights

7 takeaways

01
Petri nets are argued to be a viable and in some respects superior alternative to UML and flowchart notations for modeling game systems and game flow, especially where concurrency, conflict, and resource management are involved.
02
Most common game-design visual notations lack formal semantics, so they cannot be rigorously validated or simulated, allowing unwanted behaviors, balancing problems, and loopholes to go undetected until playtesting.
03
Petri nets pair a simple graphical notation with a mathematically defined structure that supports formal analysis for deadlocks, starvation, and precedence, as well as simulation during the design stage.
04
The argument is illustrated with an in-development strategy game inspired by the Portuguese Discoveries, modeling a native-negotiation request-and-answer process and a merchant ship voyage decomposed into hierarchical subnets for sailing, energy management, and decision making.
05
The case study uses weighted, inhibitor, and reset arcs plus hierarchical subnets to express resource depletion, conditional branching, and parallel evaluation of distance and threats.
06
Stated limitations include the inability to represent timed transitions in the tool used, declining diagram readability as complexity grows, and the need for colored Petri nets to handle varied damage types without greatly enlarging diagrams.
07
The evidence is qualitative and illustrative only; the report provides no playtesting data or comparative user study to empirically confirm the claimed advantages.

Summary

This paper argues that Petri nets offer a viable and in some respects superior alternative to conventional UML and flowchart notations for modeling game systems and game flow, particularly where concurrency, conflict, and resource management are involved. The authors contend that while visual notations are central to game design, most of them lack formal semantics and therefore cannot be rigorously validated or simulated, which allows unwanted behaviors, balancing problems, and loopholes to go undetected until playtesting. Petri nets, by contrast, combine a simple graphical notation with a mathematically defined structure that supports analysis for deadlocks, starvation, and precedence, as well as simulation during the design stage.

The argument is supported primarily through a case study drawn from an in-development strategy game inspired by the navigation and mapmaking practices of the Portuguese Discoveries. The authors model two mechanics: a request-and-answer process for negotiating with native populations, whose responses depend on the player's tone and the natives' prior opinion, and a merchant ship's voyage, decomposed into hierarchical subnets for sailing, energy management, and decision making. The diagrams illustrate how weighted arcs, inhibitor arcs, reset arcs, and hierarchical subnets can express resource depletion, conditional branching, and parallel evaluation of distance and threats. The paper acknowledges limitations, including the inability to represent timed transitions in the tool used, the difficulty of keeping complex diagrams readable as they grow, and the need for colored Petri nets to model varied damage types without exploding diagram size. The evidence is qualitative and illustrative rather than empirical, with no playtesting data or comparative user study reported.