'''Syntax diagrams''' (or '''railroad diagrams''') are a way to represent a [[context-free grammar]]. They represent a graphical alternative to [[Backus-NaurBackus–Naur Form]] or [[EBNF]]. Early books using syntax diagrams include the "Pascal User Manual" written by Niklaus Wirth <ref name="Wirth1974">[http://www.standardpascal.org/The_Programming_Language_Pascal_1973.pdf Niklaus Wirth: ''The Programming Language Pascal.'' (July 1973)]</ref> (diagrams start at page 47) and the Burroughs [[CANDE]] manual <ref name="burroughs71">http://bitsavers.org/pdf/burroughs/B6500_6700/5000318_B6700_CANDE_Oct72.pdf</ref>. In the compilation field, textual representations like BNF or its variants are usually preferred. BNF is well understood by compiler writers and compilers, but is not well understood by most users of languages. Railroad diagrams are more readily understood by most people. Some of the popularity of the [[JSON]] data interchange format is due to its representation in railroad diagrams. {{Fact|date=June 2009}}
