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