This document provides an introduction to Bakus-Naur Form (BNF), which is a formal way to describe the grammar of a language using production rules. It explains that BNF describes the allowable symbols and structure of a language without ambiguity. Production rules use symbols and define each symbol in terms of subsymbols or terminals. Terminals cannot be broken down further. An example BNF grammar for fractional numbers is provided. The document also challenges the reader to create a BNF for UK postcodes and mentions syntax diagrams as an alternative notation.

1. Bakus-Naur Form

2. What is it?
• A formal, mathematical way to
describe a language
• It describes the grammar of a
language, so that there is no
disagreement or ambiguity as to what
is allowed
• How ….?

3. Production Rules
• Symbol := alternative1 | alternative 2 …
• alternative1 := subsymbol1 | terminal
• Terminals are the end of the line, they
terminate the production process.
• The language described is the set of
all the strings you can produce by
following the production rules

4. Example BNF Grammar
<S> := ‘-’ <FN> | <FN>
<FN> := <DL> | <DL> ‘.’ <DL>
<DL> := <D> | <D> <DL>
<D> := ‘0’|’1’|’2’|’3’|’4’|’5’
|’6’|’7’|’8’|’9’
S=Start Symbol, FN = Fractional Number, DL = Digit
list, D=digit

5. Question 1

6. Question 2

7. American example

8. Challenge
• Create BNF for a UK postcode
<postcode> := <onetwolets><onetwodig><optionlet>sp<onetwodig><twolets>
<onetwolets> := <twolets> | <letter>
<twolets> := <letter><letter>
<onetwodig> := <digit> | <digit><digit>
<optionlet> : | <letter>
<letter> := a|b|c|d|e|f …….
<number> := 0|1|2 ……

9. Syntax Diagrams

10. Syntax diagram elements
Create a Syntax diagram for a Windows filename