What is a Railroad Diagram? known as Syntax diagram



A Railroad is a diagram that permits to visualize a grammar (Same as a process flow)


With RRDiagram and BNF syntax of H2 select SQL

<pre class="BNF">
'SELECT' [ 'TOP' term ] [ 'DISTINCT' | 'ALL' ] selectExpression {',' selectExpression} \
'FROM' tableExpression {',' tableExpression} [ 'WHERE' expression ] \
[ 'GROUP BY' expression {',' expression} ] [ 'HAVING' expression ] \
[ ( 'UNION' [ 'ALL' ] | 'MINUS' | 'EXCEPT' | 'INTERSECT' ) select ] [ 'ORDER BY' order {',' order} ] \
[ 'LIMIT' expression [ 'OFFSET' expression ] [ 'SAMPLE_SIZE' rowCountInt ] ] \


A Railroad diagram is made of:

  • a main diagram
  • a set of syntax diagrams.

Each diagram has an entry point and an endpoint.

It describes possible paths going through :

To belong to the language, an expression must describe a path starting from the main diagram.


  1. RRDiagram
  2. Rail Road Generator: Javascript + svg (not open source)
  3. Railroad-diagrams Javascript + svg
  4. Weltraumschaf/ebnf Php + Image, plugin dokuwiki

Others: https://npm.io/search/keyword:railroad


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