Introduction to Petri Net

ArticleDirectory

• Structure
• Action

Petri NetIs a mathematical representation of a discrete parallel system. Petri Net was invented by C. A. Petley in the 1960 s and is suitable for describing asynchronous and concurrent computer system models. Petri Net has both strict mathematical expressions and intuitive graphical expressions.

Because Petri Net can express concurrent events, it is considered as an Automation Theory. The research field tends to think that petri net is the mother of all process definition languages.

Classical Petri Net

The classic Petri Net is a simple process model with two types of nodes: library and change, directed arc, and Token.Element.

Structure

Elements of Petri Net:

• Library(Place) Circular Node
• Change(Transition) Square Node
• Directed arc(Connection) is the directed arc between the database and the change
• Token(Token) is a dynamic object in the database. It can be moved from one database to another.

Petri NetRulesYes:

• Directed arc
• There is no arc between two libraries or transitions
• The library can have any number of tokens

Action

If every changeInput Library(Input place) all have tokens, and the change isEnable). When a change is allowed, the change willOccurred(Fire ),Input Library(Input place) token is consumedOutput Library(Output place) generates a token.

Note:

• Changes occur as atoms;
• Two changes are allowed, but only one change can occur at a time;
• If a change occurs, the number of tokens in the input database is different from that in the output database;
• The Petri net is static;
• Petri NetStatusDetermined by the distribution of tokens in the database.

Two changes compete for a token.Conflict

Multiple arcs are connected to two nodes. The number of arcs between the input database and the change determines the number of tokens required for the change. The number of arcs determines the number of consumed/generated tokens.

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