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.

Agent Tcl is a transportable-agent system that is under development at Dartmouth College. A transportable agent is a named program that can migrate from machine to machine in a heterogeneous network. Such programs are apowerful tool for implementing information agents since the electronic resources in a user's information space are often distributed across a network and can contain tremendous quantities of data. Sending a user-speci c program to the network location of the resource is often the most convenient and e cient alternative. The goal of Agent Tcl is to address the weaknesses of existing transportable-agent systems. Agent Tcl will run on standard hardware, support multiple languages and transport mechanisms, provide transparent migration and communication, and provide e ective security and fault-tolerance in the uncertain world of the Internet. This paper describes the architecture of Agent Tcl and its current implementation and presents four informationmanagement applications in which Agent Tcl has proven useful. 1

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

exible and secure mobile-agent system