Extended Backus–Naur form

Ebnf-syntax-diagram

Extended Backus–Naur Form (EBNF) is a syntax notation used for the formal description of computer programming languages, data structures, and protocols. It is an extension of the Backus–Naur Form (BNF), which was developed in the 1960s by John Backus and Peter Naur. EBNF enhances BNF by providing additional constructs and notation, making it more expressive and easier to read.

Overview

EBNF is widely used in software engineering and computer science documentation to specify the grammar of programming languages. It allows the representation of the syntax rules of a language in a clear and concise manner. EBNF introduces several enhancements over BNF, including the ability to specify repetitions, optional elements, and groupings, which are essential for describing complex language syntaxes.

Syntax and Semantics

The syntax of EBNF is characterized by its use of certain symbols and constructs to define the rules of a language. These include:

• Terminal symbols: Represented by strings enclosed in quotes (e.g., "if", "while") or other specific notation. These symbols are the basic, indivisible elements of the language.
• Non-terminal symbols: Names that represent a sequence of terminal and/or non-terminal symbols (e.g., <expression>, <statement>).
• Repetition: Indicated by curly braces {} around a sequence that may repeat zero or more times.
• Optionality: Denoted by square brackets [] around an optional sequence.
• Grouping: Parentheses () are used to group sequences together, affecting the order of evaluation.
• Alternation: The vertical bar | symbol is used to separate alternatives, indicating a choice between sequences.

Examples

A simple example of EBNF might be the definition of a simple arithmetic expression:

``` <expression> ::= <term> {("+" | "-") <term>}. <term> ::= <factor> {("*" | "/") <factor>}. <factor> ::= <number> | "(" <expression> ")". <number> ::= [0-9]+. ```

This example defines an <expression> as a <term> followed by zero or more instances of either a "+" or "-" followed by another <term>. A <term> is defined similarly, with multiplication and division operations. A <factor> can be either a <number> or another <expression> enclosed in parentheses, allowing for nested expressions. A <number> is one or more digits.

Applications

EBNF is used in the design and documentation of programming languages, where it serves as a blueprint for the language's syntax. It is also used in the development of compilers and interpreters, where the EBNF description of a language can be directly translated into code that can parse programs written in the language. Furthermore, EBNF is utilized in the creation of software tools that require a precise understanding of the syntax of data formats and communication protocols.

Conclusion

Extended Backus–Naur Form is a powerful tool for describing the syntax of programming languages and other formal languages. Its expressiveness and clarity make it an essential part of the toolkit for computer scientists, software engineers, and anyone involved in the design and implementation of languages and protocols.

Extended Backus–Naur form Resources
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