1. Chalmers University of Technology (c) Boris Koldehofe Using Actors in an Interactive Animation in a Graduate Course on Distributed Systems A play (experiment) in four acts by Philippas Tsigas and Boris Koldehofe

2. Chalmers University of Technology (c) Boris Koldehofe Content Background, intention and motivation Self-Stabilisation Experiment: –Act one,..., Act four Evaluation Conclusion

3. Chalmers University of Technology (c) Boris Koldehofe Background Every year about seven one week intensive courses for graduate students are offered Courses give an overview on the research of the department Help new Ph.D students to decide on their research direction This particular course deals with research areas in distributed systems in particular self-stabilisation and fault tolerance Addresses students without background in distributed systems

4. Chalmers University of Technology (c) Boris Koldehofe Intention and Motivation Students should understand the basic concepts They should be able to verify the correctness and proof basic properties Become interested in the research topics discussed in the course

5. Chalmers University of Technology (c) Boris Koldehofe Method and Related Work Propose a dramatisation to teach Dijkstra´s self-stabilising token passing algorithm Based on the idea that animations can be useful for introducing basic concepts in distributed computing Related Work LYDIAN (1999) or ViSiDiA Dramatisation (Rifkin, 1994 and Ben- Ari, Kolikant,1999) qualitative and quantitative approaches (Kolikant, Ben-Ari, Pollack, 2000).

6. Chalmers University of Technology (c) Boris Koldehofe Arbitrary state Self-stabilisation The distributed system works correct if it is in a safe state Ensures that the system behaviour eventually stabilises to a safe subset of states regardless of the initial state Safe state One of the most active research areas in distributed computing Teaching challenges: lacking real-time metaphor and state explosion

7. Chalmers University of Technology (c) Boris Koldehofe Dramatisation of Dijkstra´s self- stabilising token passing algorithm Uses four acts, each associated with an educational topic Each act is followed by a discussion with the audience (the students) The processes are represented by a real actor. The states of processes (active/sleeping) are indicated by an actors speaking/ not speaking. The shared memory is represented by a partitioned table The value of a shared variable is represented by the number of apples inside the respective partition of the table

8. Chalmers University of Technology (c) Boris Koldehofe The perfect system Introduces the non- stabilising algorithm Explains the token passing idea P1 P2 P3 x2 x1x3

9. Chalmers University of Technology (c) Boris Koldehofe Introducing Transient Faults Malicious actor introduces multiple apples Removing apples etc. P1 P2 P3

10. Chalmers University of Technology (c) Boris Koldehofe Attempt to self-stabilisation Introduced Dijkstra´s self-stabilising algorithm Actors use an infinite supply of apples Central Basket with Apples P1 P2 P3 P1 Check: right == left P3 Check: right != left P2 Check: right != left

11. Chalmers University of Technology (c) Boris Koldehofe Interactive finalisation of the algorithm Students could interact with the system by modifying the setting of apples Critical incident: Students found bug in the wrong algorithm Students created the new rule Central Basket with Apples P1 P2 P3

12. Chalmers University of Technology (c) Boris Koldehofe Evaluation 13 Students participated in the course 11 of which helped with the evaluation of the course The overall attitude towards the animation was very positive All students thought that the animation helped a lot or fairly well to understand the algorithm Most students prefer animations with human actors compared to computer animations (7/1). Spontaneous and not predefined reactions of human beings seem to provide more information Animations in general, children game representation

13. Chalmers University of Technology (c) Boris Koldehofe Created a framework for teaching self-stabilisation Dramatisation can be a very powerful method in the learning process Useful when a complicated concept must be presented to an audience with a different background Future Work: Analyse further the difference between computer animations and dramatisation Using Virtual Actors Conclusion / Future Work