Petri Nets are a type of graph used to design and analyze concurrent distributed systems. Anything that have multiple moving parts that are dependent on each other can be modeled well with these.

There are four elements of a Petri Net:

1. States (Places)
2. Transitions
3. Arcs
4. Tokens

States are represented as circles, and are for marking discrete states. For example: On, off, a queue, etc. They hold tokens inside of them.

Transitions are represented as either Lines or Boxes. They mark a verb in the state machine. Anything that will change the current state to another state.

Arcs are represented as an arrow that points from a State to a Transition or vice versa. These are what make up the logical flow of the entire Net.

Tokens are represented as little dots that sit within the states. They mark the current state of the operating machine, and pass from state to state when an intermediate transition is "fired".

The value of using a Petri Net is that both the State and Verbs (Transitions) are treated as first class citizens. This makes them useful in graphically describing conditional logic.

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