Daniel M. Zimmerman

A hands-on look at Java mobile agents

What are the benefits and drawbacks of current Java mobile agent systems? The authors installed and evaluated three leading systems available for download from the Web: General Magics Odyssey, IBMs Aglets, and ObjectSpaces Voyager-and looked at issues such as ease of installation, feature set, documentation, and cost. We also discuss new capabilities of Java 1.1 that show promise as simple yet powerful means to create mobile agent systems. We conclude with a brief look at the ways in which mobile agents are currently being used and the limitations of todays technologies.

A Framework for Structured Distributed Object Computing

This paper presents a four-faceted framework for distributed applications that use worldwide networks connecting large numbers of people, software tools, monitoring instruments, and control devices. We describe a class of applications, identify requirements for a framework that supports these applications, and propose a design fulfilling those requirements. We discuss some initial experiences using the framework, and compare our design with other approaches.

Webs of Archived Distributed Computations for Asynchronous Collaboration

We identify the mechanisms needed to construct archivable webs of distributed asynchronous collaborations and experiments. The distinguishing feature of our approach is that the component tools, software, data, and even participants are distributed over a worldwide network. We perform a requirements analysis of an infrastructure that supports such applications, and present the Caltech Infospheres Infrastructure as a prototype that satisfies the requirements identified. In describing this prototype, we highlight the useful mechanisms provided, present an algorithm for using the Infospheres Infrastructure to perform asynchronous global snapshots for archiving, and suggest future areas of exploration.

Snapshot Processing in Streaming Environments

Computational issues related to streaming data, and in particular the monitoring and rapid correlation of multiple sources of streaming data, are becoming increasingly important in contexts ranging from business processes to crisis detection. For example, a government system to detect bioterror attacks must correlate multiple streams of possibly low-confidence data from sensors and local and national public health information networks with cues from indicators such as news and government sources indicating geographical locations, tactics and timing of possible attacks. The results of this correlation trigger appropriate responses, such as flagging information for more in-depth analysis or sending alerts to public health officials. Monitoring and correlation applications of this type are ideal for deployment on distributed computing grids, because they have high transaction throughput, require low latency, and can be partitioned into sets of small communicating computations with regular communication patterns. An important consideration in these applications is the need to ensure that, at any given time, computations are carried out on an accurate - or at least close to accurate - picture of the environment being monitored. One way of doing this, which we call snapshot processing, is to treat collections of events that occur at approximately the same time as representing a global snapshot - a valid state - of the environment. Computation on the resulting series of snapshots is much like computation on a real-time video of the entire environment. We briefly describe our model for these stream processing computations and introduce the concept of snapshot processing

Multi-user Object-Oriented Environments

Network-based computer environments emulating selected aspects of the physical world and allowing interaction among their human users first appeared in the late 1970s. These environments implemented a networked version of a role-playing fantasy game known as Dungeons and Dragons, hence their acronym MUD (Multi-user Dungeons). When it became obvious that many MUD users use the environment mainly to meet virtually with other users rather than to play games, new forms of MUDs and other types of emulated universes were developed and the term Virtual Environment (VE) was introduced to refer to all of them.

A UNITY based formalism for dynamic distributed systems

We describe Dynamic UNITY, a new formalism for the specification of dynamic distributed systems based on the UNITY formalism. This formalism allows for the specification and proof of systems where processes may be created and destroyed, and where communication links among processes may change. It also introduces asynchronous messaging as a primitive construct, to facilitate the composition of multiple programs into a larger system. We also present an example Dynamic UNITY system that illustrates the dynamic aspects of the new formalism, and outline a correctness proof for the example.