Page type: student

David A. Karr;David A. Karr;PhD Student;Department of Computer Science;Cornell University;4144 Upson Hall;Ithaca, NY 14853;Tel: (607)255-1159;Fax: (607)255-4428;E-mail: karr@cs.cornell.edu;I am a Ph.D. student in the Department of Computer Science;at Cornell University.;I am working on the;Horus project;(a layered architecture for reliable distributed systems);with;Professor Kenneth P. Birman;and;Dr. Robbert van Renesse.;My minor field is;mathematics,;concentrating in statistics.;Research Interests;[Engineering layered communication protocols];--;[Weak consistency];--;[Performance];--;[HTML/Java];Engineering layered communication protocols;My research interests include the problems of specifying,;implementing, and verifying applications;to run on distributed computer systems.;My dissertation work has concentrated on the formal;specification and verification of the properties of;Horus protocol layers.;Using the;Temporal Logic of Actions,;one can specify various;interesting fundamental properties of the protocol layers used;in Horus protocol stacks;;furthermore, one can write a formula in the assume/guarantee style;for each layer, specifying the properties it might provide at its;interfaces depending on the properties of the layers above and;below it in the stack.;One can then employ straightforward techniques to verify that a;given stack provides certain desired properties at the;top of the stack under specified conditions, even for unusual;combinations of layers or layers stacked in an atypical stacking order.;Ultimately, users of Horus and other layered communications systems;should be able to call on these verification techniques to help construct;customized stacks that omit unnecessary layers (avoiding their;associated costs), with the confidence;that the included layers and their stacking order are sufficient;to provide the desired guarantees.;This work is intended to be part of the basis for the;Securing and Hardening Horus project.;I have developed a Java applet that gives a rough demonstration;of my proposed method of;verifying the properties of Horus protocol stacks.;My initial interest in the Horus project stems from the;promise of the Horus protocol suite to provide various;guarantees of consistency to programmers in message-passing;environments where hosts may crash and messages may be delayed;or lost.;As a software development engineer who has;worked on distributed applications whose components;were prone to failure, I feel the features of Horus offer considerable;promise to application developers.;Weak consistency;While at Cornell I have become interested in the problems of;distribution of computing over wide-area networks,;and have looked into the problems of revision control of files;in a wide-area environment, and in general in a distributed;environment whose network is prone to be partitioned;into disconnected portions.;More generally, I am interested in notions of ``weak consistency'' that would;allow multiple temporarily disconnected sites to make progress concurrently.;Performance;My research at Cornell has concentrated on correctness of protocols,;but other measures such as high availability, low response time, and;efficient use of resources are clearly equally important.;A large part of the problem is the apparently randomized timing of;system loads and activity in distributed applications;(with the notable exception of those that run on dedicated parallel;machines).;This behavior also should be susceptible to some mathematical analysis,;though of a different kind (which encouraged my interest in statistics).;HTML and Java;The World Wide Web itself is an interesting distributed application;with many possibilities to explore.;I've experimented with simple ways to use hypertext to;navigate information (most of these appear in my;Web site about LEGO toys),;and I've been hacking Java applets (executable code that a;Netscape 2.0 browser can download and run),;for example a;birthday puzzle calculator.;and a tool for;verifying properties of Horus protocol stacks.;Professional Affiliations;I am a member of;IEEE,;ACM,;and;MAA.;Other Information;See;my WWW links;for other topics I find interesting or useful.;Last updated;11 June 1996.;David A. Karr /;karr@cs.cornell.edu;