PORGY: Interactive and visual reasoning with graph rewriting systems

Graph rewriting systems are easily described and explained. They can be seen as a game where one iterates transformation rules on an initial graph, until some condition is met. A rule describes a local pattern (i.e. a subgraph) that must be identified in a graph and specifies how to transform this subgraph. The graph rewriting formalism is at the same time extremely rich and complex, making the study of a model expressed in terms of graph rewriting quite challenging. For instance, predicting whether rules can be applied in any order is often difficult. When modelling complex systems, graphical formalisms have clear advantages: they are more intuitive and make it easier to visualize a system and convey intuitions about it. This work focuses on the design of an interactive visual graph rewriting system which supports graphical manipulations and computation to reason and simulate on a system. PORGY has been designed based on regular exchanges with graph rewriting systems experts and users over the past three years. The design choices relied on a careful methodology inspired from Munzner's nested process model for visualization design and validation [4].