Giuseppe Vizzari

Modeling dynamic environments in multi-agent simulation

Real environments in which agents operate are inherently dynamic—the environment changes beyond the agents’ control. We advocate that, for multi-agent simulation, this dynamism must be modeled explicitly as part of the simulated environment, preferably using concepts and constructs that relate to the real world. In this paper, we describe such concepts and constructs, and we provide a formal framework to unambiguously specify their relations and meaning. We apply the formal framework to model a dynamic RoboCup Soccer environment and elaborate on how the framework poses new challenges for exploring the modeling of environments in multi-agent simulation.

SITUATED CELLULAR AGENTS APPROACH TO CROWD MODELING AND SIMULATION

The article describes a multi-agent approach to crowd modeling and simulation. After a brief introduction of the Situated Cellular Agents model, the guidelines to the crowd modeling approach is introduced as a way to support the communication among the different actors that are part of the simulation project team. The approach is then applied to describe a complex scenario providing a blend of competitive and cooperative behavior for pedestrian agents: an underground station. A module supporting the effective 3D visualization of simulated crowd dynamics is finally introduced, as an instrument for the communication of simulation results to decision makers and nonexperts in crowd phenomena.

Towards a methodology for situated cellular agent based crowd simulations

This paper introduces a research activity aimed at the definition of a methodology to provide a solid conceptual framework for the development of simulation systems focused on crowd dynamics and based on the Situated Cellular Agent (SCA) model. After a brief introduction of the SCA Model, the general methodological approach is described. The main steps provide the definition of the spatial abstraction of the environment, the definition of its active elements, and the specification of types of mobile agents, the related behaviours with particular attention to their movement by means of the notion of utility. A case study is also briefly described in order to show how the methodology was applied in the modelling of crowd behaviour in an underground station.

Awareness in collaborative ubiquitous environments: The Multilayered Multi-Agent Situated System approach

Collaborative Ubiquitous Environments (CUEs) are environments that support collaboration among persons in a context of ubiquitous computing. This article shows how results of the research in the Multi-Agent System (MAS) area, and in particular on MAS environments, can be used to model, design and engineer CUEs, with specific reference to the management of context-awareness information. After a description of the reference scenario, the Multilayered Multi-Agent Situated System model will be introduced and applied to represent and to manage several types of awareness information (both physical and logical contextual information). Finally, three different approaches to the design and engineering of CUEs will then be introduced and evaluated.

Agent Based Modeling and Simulation

The term computer simulation is related to the usage of a computational model in order to improve the understanding of a systems behavior and/or to evaluate strategies for its operation, in explanatory or predictive schemes. There are cases in which practical or ethical reasons make it impossible to realize direct observations: in these cases, the possibility of realizing in-machina experiments may represent the only way to study, analyze and evaluate models of those realities. Different situations and systems are characterized by the presence of autonomous entities whose local behaviors (actions and interactions) determine the evolution of the overall system; agent-based models are particularly suited to support the definition of models of such systems, but also to support the design and implementation of simulators. Agent-Based models and Multi-Agent Systems (MAS) have been adopted to simulate very different kinds of complex systems, from the simulation of socio-economic systems to the elaboration of scenarios for logistics optimization, from biological systems to urban planning. This paper discusses the specific aspects of this approach to modeling and simulation from the perspective of Informatics, describing the typical elements of an agentbased simulation model and the relevant research. Multi-Agent Systems, Agent-Based Modeling and Simulation

Environments for situated multi-agent systems: beyond infrastructure

There is a lot of confusion on what the environment of a multi-agent system (MAS) comprises. Sometimes, researchers refer to the environment as the logical entity of a MAS in which the agents and other resources are embedded. Sometimes, the notion of environment is used to refer to the software infrastructure on which the MAS is executed. Sometimes, environment even refers to the underlying hardware infrastructure on which the MAS runs. n nOur research focuses on situated MASs, i.e. MASs in which agents have an explicit position in the environment. In this paper, we propose a three-layer model for situated MASs that considers agents as well as the environment as first-order abstractions. The aim of this model is to clarify the confusion between the concept of the environment and the infrastructure on which the MAS is deployed. The top layer of the model consists of the MAS application logic, the middle layer contains the software execution platform, and the physical infrastructure is located in the bottom layer. Starting from this model, we propose a classification of situated MASs based on the physical infrastructure of the MAS. We illustrate the different classes with examples from the research community and our own practice. We apply the three-layer model to each example. The models show that agents and the environment are abstractions that crosscut the three layers of the model.

Crowd Modeling and Simulation

The paper introduces a Multi Agent Systems (MAS) approach to crowd modelling and simulation, based on the Situated Cellular Agents (SCA) model. This is a special class of Multilayered Multi Agent Situated System (MMASS), exploiting basic elements of Cellular Automata. In particular SCA model provides an explicit spatial representation and the definition of adjacency geometries, but also a concept of autonomous agent, provided with an internal architecture, an individual state and behaviour. The latter provides different means of space-mediated interaction among agents: synchronous, between adjacent agents, and asynchronous among at-a-distance entities. Heterogeneous entities may be modelled through the specification of different agent types, defining different behaviours and perceptive capabilities. After a brief description of the model, its application to simple crowd behaviours will be given, and an application providing the integration of a bidimensional simulator based on this model and a 3D modelling application (3D Studio) will also be described. The adoption of this kind of system allows the specification and simulation of an architectural design with reference to the behaviour of entities that will act in it. The system is also able to easily produce a realistic visualization of the simulation, in order to facilitate the evaluation of the design and the communication with involved decision-makers. In fact, while experts often require only abstract and analytical results deriving from a quantitative analysis of simulation results, other people involved in the decision-making process related to the design may be helped by qualitative aspects better represented by other forms of graphical visualization.

Pedestrian and crowd dynamics simulation: testing SCA on paradigmatic cases of emerging coordination in negative interaction conditions

The paper presents a set of theoretical experiments performed to evaluate Situated Cellular Agent (SCA) approach within pedestrian dynamics research context. SCA is a modeling and simulation approach based on Multi Agent Systems principles that derives from Cellular Automata. In particular, we focus on two emerging phenomena (freezing by heating and lane formation phenomena) that have been empirically observed and already modeled by analytical particle-based models and Cellular Automata-based models.

WWW in the Small

The web technology is increasingly used by communities of various kinds to support their memory and the interactions among their members. In these cases the WWW can be viewed as a web of local spaces (Web in the small), each characterized by local structure and semantics. The local space can be used to provide the community members with adaptive functionalities to enhance their navigations and to promote new forms of interaction among them. The realization and management of these functionalities are sustainable since they do not require more knowledge and effort than the ones the community generates and spends to survive. The paper presents a technology, the LAW system, which is a step towards a view of the Web in the small and complements more traditional technologies supporting the current acceptation of the World Wide Web (Web in the large). The LAW system is informed by an agent based model where space and its topology are first class concepts.

Web sites as agents' environments: general framework and applications

A web site presents an intrinsic graph-like spatial structure composed of pages connected by hyperlinks. This structure may represent an environment in which agents related to visitors of the web site are positioned and moved in order to track their navigation. To consider this structure and to keep track of these movements allows the monitoring of the site and its visitors, in order to support the enhancement of the site itself through forms of adaptivity, but also to introduce new forms of interaction among registered visitors. This paper presents a model supporting the collection of information related to users behaviour in a web site, and an application supporting the proposal of hyperlinks based on the history of users movement in the web site environment. Moreover the paper briefly describes a system implementing a context-aware form of interaction, supporting the communication among visitors of a web site through the exploitation of its structure.