The Colloquium Series of the
            Department of Computer Science,
		  University of Wyoming

			presents

                    Dr. Robert Steinke
                 	   JPL       

"Blackboard Simulation, Timeline Variables, and Distributed Shared Memory"

                  Monday, April 11, 2005
	                ENG 3102
	             2:00 - 3:00 p.m.

Abstract:

Our group at JPL is currently developing a spacecraft simulation for a 
future Mars mission based on a successful blackboard type simulation of
the Mars Exploration Rovers.  Blackboard simulations are ones in which
system state is stored in a globally visible blackboard and different
actors collaborate by sharing state variables.  One enhancement in this
new simulation is the use of "timeline" variables, or variables that
explicitly record a history of values written to that variable.
Timeline variables are well suited to discrete time simulation because
the simulation time that should be associated with any write is known.
Another enhancement is that the new simulation needs to be able to run
as a distributed simulation.  We decided simply to distribute the
blackboard via a distributed shared memory system.  While looking into 
what shared memory consistency was required we realized that timeline
variables open up a whole range of possibilities and questions about how
shared memory consistency should be defined and implemented.  This talk
will describe the possibilities and what we actually wound up designing.