Event Structures for Petri nets with Persistence
2018
Event structures are a well-accepted model of concurrency. In a seminal paper
by Nielsen, Plotkin and Winskel, they are used to establish a bridge between
the theory of domains and the approach to concurrency proposed by Petri. A
basic role is played by an unfolding construction that maps (safe) Petri nets
into a subclass of event structures, called prime event structures, where each
event has a uniquely determined set of causes. Prime event structures, in turn,
can be identified with their domain of configurations. At a categorical level,
this is nicely formalised by Winskel as a chain of coreflections.
Contrary to prime event structures, general event structures allow for the
presence of disjunctive causes, i.e., events can be enabled by distinct minimal
sets of events. In this paper, we extend the connection between Petri nets and
event structures in order to include disjunctive causes. In particular, we show
that, at the level of nets, disjunctive causes are well accounted for by
persistent places. These are places where tokens, once generated, can be used
several times without being consumed and where multiple tokens are interpreted
collectively, i.e., their histories are inessential. Generalising the work on
ordinary nets, Petri nets with persistence are related to a new subclass of
general event structures, called locally connected, by means of a chain of
coreflections relying on an unfolding construction.
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