A technique based on recursive hierarchical state machines for application-level capture of agent execution state

The capture of the execution state of agents in agent-based and multi-agent systems is a system feature needed to enable agent checkpointing, persistency and strong mobility that are basic mechanisms supporting more complex, distributed policies and algorithms for fault tolerance, load balancing, and transparent migration. Unfortunately, the majority of the currently available platforms for agents, particularly those based on the standard Java Virtual Machine, do not provide this important feature at the system-level. Several system-level and application-level approaches have been to date proposed for agent state execution capture. Although system-level approaches are effective they modify the underlying virtual machine so endangering compatibility. Conversely, application-level approaches do not modify any system layer but they provide sophisticated agent programming models and/or agent converters that only allow a coarse-grain capture of agent state execution. In this paper, we propose an application-level technique that allows for a programmable-grain capture of the execution state of agents ranging from a per-instruction to a statement-driven state capture. The technique is based on the Distilled State-Charts Star (DSC*) formalism that makes it available an agent-oriented type of recursive hierarchical state machines. According to the proposed technique a single-threaded agent program can be translated into a DSC* machine by preserving its original semantics. Although the proposed technique can be applied to any agent program written through an imperative-style programming language, it is currently implemented in Java and integrated into the JADE framework, being JADE one of the most diffused agent platforms. In particular, agents, which are specified through a generic Java-like agent language, are translated into JADE agents according to the JADE DSCStar-Behaviour framework. A simple yet effective example is used to illustrate the proposed technique.