Petri Nets

1
Mathematics study interesting, consistent
structures
Engineering build practicable, useful structures
Computer Science ??
Carl Adam Petri Computing as a science could be
modelled after physics
Frederick P. Brooks, Jr. The computer
scientist as toolsmith
Physics predict measure real world structures
Christopher Strachey .. the separation of
practical and theoretical work is artificial
and injurious.
Frederick P. Brooks, Jr. "The scientist builds
in order to study, the engineer studies in order
to build"
2
Petri Nets

• Concurrency and causality
• -a guided tour-

Claus Reinke Computing Lab, UKC
3
From automata ...
3
2
1
Product automaton (?meta-level modelling)
One lift
4
to Petri nets
explicit transitions
3
concurrent subsystems
2
explicit synchronisation
1
explicit communication
Distributed state, local transitions
One lift
A passenger
local conflict
5
From FA to CPN - a micro-introduction
A
B
concurrency
6
Lifts again, with place/transition-nets
3
2
1
Two lifts
Three passengers
two nets, folded in one
7
Lifts, yet again, with high-level nets
3
(l,ps)
(l,ps)
max 2
(l,ps)
(l,ps)
max 2
2
(l,ps)
(l,ps)
(l,ps)
(l,ps)
1
Passengers
Two lifts