Syntax diagrams (or railroad diagrams) are a way to represent a context-free grammar. They represent a graphical alternative to Backus–Naur form, EBNF, Augmented Backus–Naur form, and other text-based grammars as metalanguages.

Syntax diagrams are one way of writing algorithms. If you look closely at the gibberish diagrams, you will see all four of the basic structures of algorithms represented.

Syntax diagrams are drawings that illustrate valid SQL syntax. To read a diagram, trace it from left to right, in the direction shown by the arrows. Commands and other keywords appear in UPPERCASE inside rectangles. Type them exactly as shown in the rectangles. Parameters appear in lowercase inside ovals. Variables are used for the parameters.

Understanding Syntax Diagrams This section describes how to read the syntax diagrams. To read a syntax diagram follow the path of the line. Read from left to right and top to bottom. The ►►─── symbol indicates the beginning of a syntax diagram. The ───► symbol, at the end of a line, indicates that the syntax diagram continues on the next line.