Timed event system DEVS (Discrete Event System Specification), a formalism for modeling and analyzing general systems, was invented by Bernard P. Zeigler published in his first book released in 1976.
DEVS abbreviating Discrete Event System Specification is a modular and hierarchical formalism for modeling and analyzing general systems that can be discrete event systems which might be described by state transition tables, and continuous state systems which might be described by differential equations, and hybrid continuous state and discrete event systems. The DEVS formalism was invented by Bernard P. Zeigler, who is emeritus professor at the University of Arizona. DEVS was introduced to the public in Zeigler's first book, , in 1976, while Zeigler was an associate professor at University of Michigan. DEVS is a timed event system. 
