An information agent manages all or a portion of a user's information space. The electronic resources in this space are often distributed across a network and can contain tremendous quantities of data. Mobile agents provide efficient access to such resources and are a powerful tool for implementing information agents. A mobile agent is an autonomous program that can migrate from machine to machine in a heterogeneous network. By migrating to the location of a resource, the agent can access the resource efficiently even if network conditions are poor or the resource has a low-level interface. Telescript is the best-known mobile-agent system. Telescript, however, requires the programmer to learn and work with a complex object-oriented language and a complex security model. Agent Tcl, on the other hand, is a simple, flexible, and secure system that is based on the Tcl scripting language and the Safe Tcl extension. In this paper we describe the architecture of Agent Tcl and its current implementation.

Abstract. Mobile-agent systems must address three security issues: protecting an individual machine, protecting a group of machines, and protecting an agent. In this chapter, we discuss these three issues in the context of D’Agents, a mobile-agent system whose agents can be written in Tcl, Java and Scheme. (D’Agents was formerly known as Agent Tcl.) First we discuss mechanisms existing in D’Agents for protecting an individual machine: (1) cryptographic authentication of the agent’s owner, (2) resource managers that make policy decisions based on the owner’s identity, and (3) secure execution environments for each language that enforce the decisions of the resource managers. Then we discuss our planned market-based approach for protecting machine groups. Finally we consider several (partial) solutions for protecting an agent from a malicious machine. 1

This paper presents a high-level framework for analysing and designing intelligent agents. The framework's key abstraction mechanism is a new computer level called the Social Level. The Social Level sits immediately above the Knowledge Level, as defined by Allen Newell, and is concerned with the inherently social aspects of multiple agent systems. To illustrate the working of this framework, an important new class of agent is identified and then specified. Socially responsible agents retain their local autonomy but still draw from, and provide resources to, the larger community. Through empirical evaluation, it is shown that such agents produce both good system-wide performance and good individual performance. 1. INTRODUCTION The number of multi-agent systems being designed and built is rapidly increasing as software agents gain acceptance as a powerful and useful technology for solving complex problems (Chaib-draa, 1995; Jennings, 1994; PAAM, 1996). As applications become more comple...

This paper argues that complex, embedded software agent systems are best constructed with parallel, layered architectures. These systems resemble Minskian Societies of Mind and Brooksian subsumption controllers for robots, and they demonstrate that complex behaviors can be had via the aggregates of relatively simple interacting agents. We illustrate this principle with a distributed software agent system that controls the behavior of our laboratory's Intelligent Room. Introduction This paper argues that software agent systems that interact with dynamic and complex worlds are best constructed with parallel, layered architectures. We draw on Brooks' subsumption architecture (Brooks, 1985) and Minsky's Society of Mind (Minsky, 1986) theory to dispel the notion that sophisticated and highly capable agent systems need elaborately complex and centralized control. Towards this end, we present an implemented system of software agents that forms the backbone of our laboratory's "Intelligent Ro...

Mobile agents are programs that can move through a network under their own control, migrating from host to host and interacting with other agents and resources on each. We argue that these mobile, autonomous agents have the potential to provide a convenient, e cient and robust programming paradigm for distributed applications, particularly when partially connected computers are involved. Partially connected computers include mobile computers such as laptops and personal digital assistants as well as modem-connected home computers, all of which are often disconnected from the network. In this paper, we describe the design and implementation of our mobile-agent system, Agent Tcl, and the speci c features that support mobile computers and disconnected operation. These features include network-sensing tools and a docking system that allows an agent to transparently move between mobile computers, regardless of when the computers connect to the network. 1

This paper explores the role of the traditional computational metaphor in our thinking as computer scientists, its influence on epistemological styles, and its implications for our understanding of cognition. It proposes to replace the conventional metaphor --- a sequence of steps --- with the notion of a community of interacting entities, and examines the ramifications of such a shift on these various ways in which we think.

Agent Tcl is a simple itinerant-agent system that runs on Unix workstations and allows the rapid development of complex agents [Gra95, Gra96]. Although Agent Tcl currently lacks the features of commercial systems such asTelescript [Whi94], it is an e ective platform for experimentation with itinerant agents and for the development of small to medium-sized applications. Agent Tcl agents

In this report, we propose a model and an associated agent platform to deal with multi-agent system heterogeneity by introducing a way to structure groups of agents and take advantage of simultaneous contexts and models. This approach uses the concepts of multiple groups and roles to introduce structure within different multi-agent systems. The platform based on this model is made of minimal agent microkernels. Basic services like migration, distributed message passing, security are provided by platform agents for maximal flexibility. The componential interface model allows variations in platform use and appearence. The platform is written in Java and support all major computer systems.

Worldwide applications exist in an environment that is inherently distributed, dynamic, heterogeneous, insecure, unreliable, and unpredictable. In particular, the latency and bandwidth of network connections varies tremendously from place to place and time to time, particularly when considering wireless networks, mobile devices, and satellite connections. Applications in this environment must be able to adapt to di erent and changing conditions. We believe that transportable autonomous agents provide an excellent mechanism for the construction of such applications. We describe our prototype transportable-agent system and several applications. 1 Transportable autonomous agents A transportable autonomous agent is a named program that can migrate from machine to machine in a heterogeneous network. The program chooses when and where to migrate. It can suspend its execution, move its code and state to another machine, and resume execution on the new machine. Transportable autonomous agents are well suited for the construction of worldwide applications for two reasons: They are transportable. In the traditional client-server paradigm, the client code communicates with the server code to access data and resources on the server's machine. For many applications, however,

One of the paradigms that has been suggested for allowing efficient access to remote resources is transportable agents. A transportable agent is a named program that can migrate from machine to machine in a heterogeneous network. The program chooses when and where to migrate. It can suspend its execution at an arbitrary point, transport to another machine and resume execution on the new machine. Transportable agents have several advantages over the traditional client/server model. Transportable agents consume less network bandwidth and do not require a connection between communicating machines -- this is attractive in all networks and particularly attractive in wireless networks. Transportable agents are a convenient paradigm for distributed computing since they hide the communication channels but not the location of the computation. Transportable agents allow clients and servers to program each other. However transportable agents pose numerous challenges such as security, privacy and...