OOPN/PNtalk basics

• Object oriented Petri nets (OOPN) is a formalism and PNtalk is a language based on OOPN.

• It was developed for modeling and prototyping distributed systems. It is based on active objects communicating by message sending. There is both inter and intra object concurrency in OOPN.

• Objects are described by high-level Petri nets. Petri nets contain references to objects in form of tokens.

• Object model and net inscription language are strongly inspired by Smalltalk. Message sending is specified by transition inscriptions. PNtalk objects are fully compatible with Smalltalk objects and it is possible to mix Smalltalk and PNtalk objects in applications.

Roots:

• Hierarchical Petri Nets
  • dynamic instantiation of nets by means of invocation trassition

• Smalltalk
  • pure object orientation, simple and powerfull language, system

• Concurrency and object-orientation
  • homogenous connection of objects and processes
  • dynamic process structure,
  • implicit instanciation of methods.

PNtalk's view on systems can be explained in time diagram of a system:

• System contain objects. One of these objects is the initial (primary) object which exists all the time the system exists. The system contains only such objects that are reachable (by references) from the initial object.

  
  
  

• An object contain processes of methods. One of these methods is an implicit method describing object's own activity. It exists during the object life time. Other methods react to incomming messages.