Problem Solving: Backus-Naur Form
Backus-Naur Form (also known as Backus Normal Form (BNF) or BNF for short) is a notation technique to express syntax of languages in computing. The expression is put in lists and can be used to see if syntax that is written is valid. Backus-Naur means "not in normal form compared to convention".
Structure and Layout[edit | edit source]
Symbols[edit | edit source]
BNF is represented using the following symbols:
::= 'is defined as' | 'or' <> category names
The way that these symbols are laid out are as such:
<Parent Expression> ::= <Child Expression 1> | <Child Expression 2>
In plain English, the expression above means "The parent expression is defined as the child expression 1 or the child expression 2". This means that to make up the parent expression, it must have a child expression and a child expression is made up of other things.
Example[edit | edit source]
In this example, The BNF structure is breaking down the syntax to create
<Address> ::= <House Number> <Street Name> <Town Name> <City Name> <Country> <Postcode> | <House Number> <Street Name> <City Name> <Country> <Post Code>
<Postcode> ::= <Area Code> <Street Code> <Area Code> ::= <City Prefix> <digit> | <City Prefix> <digit> <digit> <Street Name> ::= <Name> <Street Type> <Flat Number> ::= <character> | <digit> <House number>::= <digit> | <digit> <House number> <Street Type> ::= <string> <City Prefix> ::= <string> <Street Code> ::= <string> <Town Name> ::= <string> <City Name> ::= <string> <Country> ::= <string> <Name>::= <string>
Practice Questions[edit | edit source]