Using actors in an interactive animation in a graduate course on distributed system

We describe and evaluate an experiment where actors were used to simulate the behaviour of processes in a distributed system in order to explain the concept of self-stabilisation in a graduate course on distributed systems.A self-stabilising system is one that ensures that the system's behaviour eventually stabilises to a safe subset of states regardless of the initial state. Protocols satisfying this elegant property, which enables a system to recover from transient failures that can alter the state of the system, are often hard to understand, especially for students that have not studied distributed computing and systems before.The experiment was part of an introductory course on distributed computing and systems for graduates in October 2000. The purpose of this interactive animation was to introduce to the students the basic concepts behind self-stabilisation (eligible states, transient faults, execution convergence) before their formal introduction.All of the students had a degree either in mathematics or computing science and had taken a course on algorithms before. However, most of the students did not have a background in distributed systems or distributed algorithms. The latter was not only the motivation for preparing this method of presentation but also what made this a challenging effort.The feedback from the class was that the concept and this teaching method were very well received. We could observe that their understanding evolved to the point that they were able to successfully come up with ideas for solutions and argue for/prove their correctness. As suggested in [1], dramatisation of executions can help the students to understand new issues and complications. This work shows that this is true even for graduate level courses. In our experiment we could conclude that dramatisation can be almost as powerful as a programming exercise in the teaching process; sometimes even more efficient, especially when we need to teach new concepts to an audience with diverse educational backgrounds. In analysing the results of our method we make a combination of the qualitative and quantitative approaches [4].