A computing device for state transitions of recursive state machines and a computer-implemented method for the definition, design and deployment of domain recursive state machines for computing devices of that type; such devices are intended for the simulation of large systems involving human and automated components, particularly the type generally called “Enterprise Applications”; such devices are also applicable to a much wider range of fields, such as cognitive modelling or robotics. The commonality between the computing device and the computer-implemented method is the Subject Predicate Object Protocol (SPOP) which is used to capture instructions by the computer-implemented method for the definition, design and deployment of recursive state machines and also is the protocol used by the computing device for state transitions of recursive state machines to communicate inbound and outbound events based on the captured instructions.