Railroad Diagrams (or Syntax Diagrams)

Railroad diagrams are a way to visualize context-free grammars.

How to Read

You read the diagram from left to right and from top to bottom. The diagram is a visual representation of a context-free grammar. The diagram shows the rules of the grammar and how they are connected.

The following conventions are used:

• The following diagram shows values A, B and C, which must be specified. The required values are defined on the main line of the diagram. (ABNF: and = A B C)

• The following diagram shows the optional value A. The value can be bypassed by following the empty path. (ABNF: opt = [A] B )

• In the example below A, B and C are options. The value can be chosen from the options. (ABNF: or = A / B / C)

Example

References

• Niklaus Wirth