Petri Nets

[Mark S. Miller <mark>]

I know a bit about Petri Nets.  However, I can't figure any way in
which they would be used to model security systems.  They are quite an
interesting formalism for modeling fine-grained interacting concurrent
behavior (sort of like asyncronous communicating state machines but
different).  The can also be seen as a machine for accepting a
grammer, like state machines are for regular expressions; stack
machines are for BNF; and Turing machines are for context sensitive
grammers.  As such they are strictly more powerful than state
machines, strictly less powerful than Turing machines, and neither
more nor less powerful than stack machines/BNF (overlapping circles on
the Venn diagram).

I skooled miselph in all this from an excellent book which I can lend
to anyone interested (except that I can't find it just now)  $=]  `_'