State of the Chart

You are here

Prof. David Harel wrote the industry standard

It is unusual for theoretical mathematicians to indulge in brain surgery, and certainly not recommended without prior training. "I was trying to open up engineers' skulls and mess around to see how they think." The accent here is on "see." Thus, the Statecharts visual language was born.

Professor David Harel is one of three recipients of the first Prime Minister's Prize for Software, awarded for his Statecharts language. The concept allows engineers and designers to visually describe the workings of complex systems; it's become the standard for computerized engineering projects worldwide.

In 1983, Harel was comfortably installed as a tenured faculty member in the Institute's Department of Applied Mathematics after completing degrees at Bar-Ilan and Tel Aviv Universities, with a Ph.D. from MIT ­ earned in an as-yet unrivaled MIT record of one year and eight months.

When Israel Aircraft Industries called with an urgent request for help with the Lavi fighter jet project, Harel jumped at the chance. Apparently, there was a communications breakdown between the aircraft designers and the subcontractors charged with building parts for the bird. A totally new approach was desperately needed to cut down on the mammoth 1,000-page instruction manual, to increase clarity and simplicity. For a complex system such as an airplane, "There are zillions of scenarios and you can't just list them all and expect people to understand and go from there. I would ask 'deep and profound' questions like 'What happens if I press this button?'"

Sometimes they couldn't respond; many issues hadn't been previously raised. Harel took notes, simplifying what he saw, read and heard around him, developing his own generic descriptive language.

While writing and working at the mathematics of these descriptions, Harel was also adding illustrations. "I would doodle on the side. I'd tell them, 'Actually, what you are saying is we have this and this.' The pictures started to become more elaborate. Gradually the text became less important and we simply stopped using it."

Statecharts' popularity snowballed through word-of-mouth reports and the lectures Harel began delivering upon acknowledging the originality of his own language. He started publishing on the subject in the scientific literature. The next step was the setting up of a private company in 1984 when he and his colleagues developed Statemate, a sophisticated Statecharts-based software tool for engineers to simulate complex systems on computer.

Harel has continued refining Statecharts. A second software tool, Rhapsody, was released in early 1997. Statecharts' place in the history books is now assured with its status as one of the three basic components of a new software development approach called Unified Modeling Language (UML). UML has recently been announced as the industry standard for object-oriented analysis and design.

Statecharts can be thought of as the visual punch behind the majority of computerized engineering projects, from aircraft to cellular telephones, BMWs to the Pathfinder Mars probe. "I even heard recently," laughs Harel, "that it's being used to design the controller for flushing toilets on Lufthansa aircraft!" What greater compliment could there be for an amateur brain surgeon?