Chih-Chun Chen

A formalism for multi-level emergent behaviours in designed component-based systems and agent-based simulations

There currently exists no means of specifying or analysing specific emergent behaviours in designed multi-component systems. For this reason, important questions about the lower level mechanisms giving rise to emergent behaviours cannot be resolved.

Identifying Multi-Level Emergent Behaviors in Agent-Directed Simulations using Complex Event Type Specifications

Agent-directed simulations (ADS) are used in many domains to study complex systems. These are systems where non-linear effects can result from these emergent behaviors, making them difficult to analyze and predict. Correspondingly, in ADS, as well as explicitly specified behaviors of individual agents, higher level behaviors can emerge spontaneously from agent action sequences and agent—agent interactions. We have previously introduced the complex event formalism for specifying emergent behaviors in dynamically executing ADS [1, 2]. Based on the formalism, we also described a method for detecting and analyzing emergent behaviors in multi-agent simulations, giving us an effective means of studying, and a more reliably way of predicting, these systems. Complex event types define sets of multi-dimensional structures of interrelated events arising from the actions of one or more agents. They are therefore directly related to the agent specifications, which determine the behavior of individual agents. Although the abstract constructs of the formalism have already been introduced in [1] and [2], they have not yet been related to a specific agent-based specification language. Here, we define the constructs in terms of the X-machine formalism, which is widely used to specify multi-agent systems. This extends the existing X-machine framework to model higher level emergent behaviors as well as agent-level state transitions. Thus, emergent behaviors at any level of abstraction can be specified for detection and analysis in a dynamically executing ADS.

Multi-level behaviours in agent-based simulation: colonic crypt cell populations

Agent-based modelling and simulation is now beginning to establish itself as a suitable technique for studying biological systems. However, a major issue in using agent-based simulations to study complex systems such as those in Systems Biology is the fact that simulations are ‘opaque’. While we have knowledge of individuals’ behaviour through agent rules and have techniques for evaluating global behaviour by aggregating the states of individuals, methods for identifying the interactive mechanisms giving rise to this global behaviour are lacking. Formulating precise hypotheses about these multi-level behaviours is also difficult without an established formalism for describing them. The complex event formalism allows relationships between agent-rule-generated events to be defined so that behaviours at different levels of abstraction to be described. Complex event types define categories of these behaviours, which can then be detected in simulation, giving us computational method for distinguishing between alternative interactive mechanisms underlying a higher level behaviour. We apply the complex event formalism to an agent-based model of cell populations in the colonic crypt and demonstrate how competition and selection events can be identified in simulation at both the individual and clonal level, allowing us to computationally test hypotheses about the interactive mechanisms underlying a clone’s success.

Complexity and Emergence in Engineering Systems

The purpose of this chapter is to introduce the reader to the key concepts of complexity and emergence, and to give an overview of the state of the art techniques used to study and engineer systems to exhibit particular emergent properties. We include theories both from complex systems engineering and from the physical sciences. Unlike most reviews, which usually focus solely on one of these, we wish to analyse the ways in which they relate to one another, as well as how they differ, since there is often a lack of clarity on this.