Using Behavior Trees to Model the Autonomous Shuttle System

Abstract

The requirements for problems like the Autonomous Shuttle Transport System are relatively easy to state informally and loosely in natural language. The question is how to use this information effectively to guide the development of a system that satisfy the original intent, clarify the original intent where necessary, identify defects in stated requirements and at the same time manage the complexity of the problem. Progress is possible once we recognize that individual functional requirements represent fragments of behaviour, while a design that satisfies a set of functional requirements represents integrated behaviour. This perspective admits the prospect of constructing a design out of its requirements. A formal representation for individual functional requirements, called behavior trees makes this possible. Behavior trees, derived by rigorous word-by-word translation from individual functional requirements stated in natural language, may be composed, one at a time, to create an integrated design behavior tree (DBT). When we apply translation and integration for the original set of high-level requirements for the Shuttle System we discover they are behaviourally incomplete. Integration constructively forces us to confront and resolve the missing requirements problems at the earliest possible time in the development phase. Once this is done we should have a complete, fully integrated DBT. We can then transition from this problem domain representation directly and systematically to a solution domain representation of the component architecture of the system and the behaviour designs of the individual components that make up the system oth are emergent properties of a DBT.