ABSTRACTING INTERACTION PATTERNS:
            A HIGH-LEVEL MODEL OF CONCURRENCY FOR EVOLVING SYSTEMS

                       Prof. Gul A. Agha
                Director, Open Systems Laboratory
                  University of Illinois, Urbana

ABSTRACT:

The Actor model provides flexible mechanisms for modeling and building
open distributed systems.  Considerable research has been done on the
semantics of actors and their application to open distributed systems.
Useful results on the equivalence of configurations, their
composition, and encapsulation, have been derived, and powerful proof
techniques developed.  However, it is clear that such results are not
sufficient to address the challenge of building and reasoning about
complex distributed systems.  In order to model complex systems, it is
necessary to abstract over patterns of interaction between groups of
actors and thereby separate concerns about availability, reliability,
real-time, etc. from the application code.  I will describe a number
of programming language constructs such as actorspaces, synchronizers,
real-time synchronizers, and protocols which abstract over interaction
patterns.  I will then discuss open problems in providing a formal
model for such language constructs.