Len, (01)
The main point of my previous note was not Petri nets, but the
pi-calculus, which is most definitely *not* a closed system. (02)
Some comments: (03)
LY> ...States are not necessarily related to activities or events. (04)
That point is rather cryptic and vague. The concepts of State,
Process, and Event are abstractions from a continuous physical
world, and there are many different ways of making such abstractions.
See the following article for a brief discussion of the issues: (05)
http://www.jfsowa.com/ontology/causal.htm
Processes and Causality (06)
In particular a state in a Petri net can be the effect of many
different transitions, or it might be a state that just happens
to be true without any known cause (although it is unlikely that
any state in the real world can come to pass without some cause). (07)
In any case, the following conclusion does not follow: (08)
LY> This means that traditional object life-cycle models are inadequate. (09)
I have no idea what "this" refers to or what connection the author
assumed. (010)
LY> Traditional (Petri-net based) models of object life-cycles model
> closed systems and so assume that a state results from a transition. (011)
I will certainly admit that a major limitation of Petri nets is that
they are based on a fixed graph of state and transition types. (012)
But the main point of my previous note was that the pi-calculus is
a *generalization* of Petri nets that allows nodes and links in
the graph to be created and destroyed dynamically. That makes it
very different from a closed system. (013)
LY> I believe that in principle stateless protocols are not sufficient
> to support SOA. The alternative approaches are generally known as
> "distributed shred memory" had been researched for a long time,
> but were not economically feasible until now. (014)
Pi-calculus is ideal for representing such systems. (015)
John (016)
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