Block Diagrams for Modeling and Design

Professor Edward A. Lee
UC Berkeley

Friday, October 24th, 1997
Hogan Room, 531 Cory Hall
4:00-5:00 p.m.


Visual depictions of electronic systems have always held a strong human appeal, making them extremely effective in conveying information about a design. A few attempts to use such depictions to completely and formally specify systems have succeeded, most notably in circuit design, where schematic diagrams can capture all of the essential information needed to implement some systems. Others have failed dramatically, for example flowcharts for capturing the behavior of software. Recently, a number of innovative visual formalisms have been garnering support, including visual dataflow, hierarchical concurrent finite state machines, and object models. This talk focuses on the subset of these that are recognizable as "block diagrams." Such diagrams represent concurrent systems, but there are many possible concurrency semantics. Formalizing the semantics is essential if these diagrams are to be used for system specification and design.

This talk explores some of the possible concurrency semantics, arguing that their strengths and weaknesses make them complementary rather than competitive, so that no single model is likely to emerge as a universally useful model. I will also describe some recent innovations where concurrency models are combined with automata for sequential control. So-called hybrid systems are a special case of such combinations.