Come, Let’s Play

David Harel is the Dean of the Faculty of Mathematics and Computer Science at the Weizmann Institute of Science in Israel. He is also co-founder of I-Logix, Inc., Andover, MA, and of SenseIT Technologies, Ltd. (DigiScents Israel). His research interests are in theoretical computer science (especially computability, automata theory and logics of programs), and in software and systems engineering (especially specification and modeling, object-oriented analysis and design, and visual languages), as well as the aesthetic layout of diagrams, clustering algorithms and the synthesis and communication of smell. He is the inventor of the language of statecharts (1983), was part of the team that designed the Statemate (1984-1987) and Rhapsody (1997) tools, and was co-inventor of LSCs (1998). His work is central to the behavioral aspects of the UML. He devotes part of his time to expository work: In 1984 he delivered a lecture series on Israeli radio, and in 1998 he hosted a series on Israeli television; some of his writing is intended for a general audience (see, for example, Computers Ltd.: What They Really Can't Do , Oxford University Press, September 2000). He has received a number of awards, including ACM's Karlstrom Outstanding Educator Award in 1992, and the 1997 Israeli Prime Minister's Award for Software. His book, Algorithmics: The Spirit of Computing (Addison-Wesley, 1987, 2nd. edn. 1992) was the Spring 1988 Main Selection of the Macmillan Library of Science. He is a Fellow of the ACM and of the IEEE.

The design of reactive systems is one of the most challenging problems in computer science. This books starts with a critical insight to explain the difficulty of this problem: there is a fundamental gap between the scenario-based way in which people think about such systems and the state-based way in which these systems are implemented. The book then offers a radical proposal to bridge this gap by means of playing scenarios. Systems can be specified by playing in scenarios and implemented by means of a Play-Engine that plays out scenarios. This idea is carried out and developed, lucidly, formally and playfully, to its fullest. The result is a compelling proposal, accompanied by a prototype software engine, for reactive systems design, which is bound to cause a splash in the software-engineering community. Moshe Y. Vardi, Rice University, Houston, Texas, USA Scenarios are a primary exchange tool in explaining system behavior to others, but their limited expressive power never made them able to fully describe systems, thus limiting their use. The language of Live Sequence Charts (LSCs) presented in this beautifully written book achieves this goal, and the attached Play-Engine software makes these LSCs really come alive. This is undoubtedly a key breakthrough that will start long-awaited and exciting new directions in systems specification, synthesis, and analysis. Gerard Berry, Esterel Technologies and INRIA, Sophia-Antipolis, France The approach of David Harel and Rami Marelly is a fascinating way of combining prototyping techniques with techniques for identifying behavior and user interfaces. Manfred Broy, Technical University of Munich, Germany

• I. Prelude.- 1. Introduction.- 2. Setting the Stage.- 3. An Example-Driven Overview.- 4. The Model: Object Systems.- II. Foundations.- 5. The Language: Live Sequence Charts (LSCs).- 6. The Tool: The Play-Engine.- III. Basic Behavior.- 7. Variables and Symbolic Messages.- 8. Assignments and Implemented Functions.- 9. Conditions.- 10. Branching and Subcharts.- IV. Advanced Behavior: Multiple Charts.- 11. Executing Multiple Charts.- 12. Testing with Existential Charts.- V. Advanced Behavior: Richer Constructs.- Loops.- Transition to Design.- Classes and Symbolic Instances.- Time and Real-Time Systems.- Forbidden Elements.- VI Enhancing the Play-Engine.- Smart Play-Out (with H. Kugler).- Inside and Outside the Play-Engine.- A Play-Engine Aware GUI Editor.- Future Research Directions.- VII Appendices.- A. Formal Semantics of LSCs.- A.1 System Model and Events.- A.2 LSC Specification.- A.3 Operational Semantics.- B. XML Description of a GUI Application.- C. The Play-Engine Interface.- C.1 Visual Basic Code.- D. The GUI Application Interface.- D.1 Visual Basic Code.- E. The Structure of a (Recorded) Run.- References.