Modelling Based on Petri Nets

Why petri nets

Petri Nets can be used to a rigorously defined system
They are often used for distributed system (several sub system acting independently) and resource sharing systems
Since there are many transitions in patron that activate at the same time, They are nondeterministic

The state of a Petri Net is determined by distribution of tokens over the places
A transition in Petri Net can have multiple input and output
Enabling condition: A transaction is enabled if each of the input places contains tokens (more than required by weight)
Firing: And enabled transition may fire, that consuming tokens from the input and producing tokens for the output places.
- Firing is atomic (only one transition fires at a time, Even if more than one is enabled)
A transition without any input can fire at any time
A transition without output will consume or delete the incoming tokens
Conflict: Two transaction fight for the same token, Even if they were too token in the input place. Who will fire first is nondeterministic.

States of a process can be modelled by tokens in places, And transition leading from one state to another modelled by Petri Net transitions.

Tokens can represent resources like human, goods, machines and information or condition.
Places represent buffers, channels, etc.
Transition represent events, transformations or transportation.

High-level petri nets are extended with - Color - Time - Hierarchy