This is a NASA sponsored research project. The goal of the project is to develop publicly accessible data sets and databases for use by scientists, planners, the general public, and other groups.

My role in the project is, along with other members of the group, to research and to provide efficient mechanisms to distribute and transfer data. One important characteristics of these data is that they are mostly generated and used by other geographic information system and remote sensing software such as ARC/INFO and ER-MAPPER.

This project is ongoing.

Related resources on the Internet:

Digital Library Initiatives

Most programmers depend on repeatable behavior of the program to locate bugs of the program. In a sequential program, the execution of the program can easily be repeated. In a distributed program, however, the execution order of the program components varies from one run to another due to external factors such as network delay. It is very difficult, often impossible, to repeat the same sequence of execution. This makes the debugging of distributed program very difficult.

This research focus on one tool that can aid debugging in distributed programming. The tool is written in such a way that the network functions of a distributed program can be replaced with the software modules that communicate through memory. The programmer can test the distributed program on a single machine when debugging. The network activities are simulated. The debugging programmer can use different random seed to try difference sequences of program execution. But each one is repeatable. In this way, most of the bugs can be found when debugging on a single machine. The programmer can then link the distributed program with real network library. No internal program changes are required, only linking with different libraries.

This project is ongoing.

In this research, we started with investigating the issue of space utilization in distributed simulation. Using the fact that events in the event list form a forest, deleting events when rolling back can be realized by a tree traversal algorithm. This can effectively save space used for storing such information as incoming message and separate state information. This concept can be applied to the class of problems where process does not deposit events or messages on other processes.

We then studied the feasibility and efficiency of implementing distributed simulation in the environment of cluster of workstations. We found that though frequent communications increase the delay and reduce the efficiency, they can also reduce the number of rollbacks. When more communications are present, optimistics simulation is more efficient; when very little communciations take place, conservative simulation seems more effective.

This project is in its final stage. I am trying to write a summary paper. A list of my publications in this work can be found here .