Extracting high-level information from Petri nets: a railroad case

We show how useful simulation and control applications can be built on Petri nets by
adding an object-oriented transformation framework called “views”. Petri nets were
integrated into the Common Lisp Object System in such a way that the usual objectoriented
features, such as classes, object creation, encapsulation, and inheritance, also
work for Petri nets. This modified object system allows views to be implemented as
collections of methods on the modified classes. Views are used to extract and present
relevant domain specific aspects of a Petri net model. This functionality was implemented
in our prototype Petri net engine called Andromeda. As a test case we modeled
the Oslo subway as a hierarchy of railroad specific components, and built a composite
view showing train and passenger movements.