4.4.3 - ToC (Context-Free Languages)

Question 1

What is Backus-Nour Form

Answer 1

A formal, mathematical way of defining syntax unambiguously

Question 2

What does BNF consist of

Answer 2

Terminal Symbols
Production Rules
Non-Terminal Symbols

Question 3

What are terminal symbols/elements

Answer 3

Elements that cannot be broken down anymore e.g, a letter

Question 4

What are non terminal symbols or elements

Answer 4

Elements that are defined by constants (i.e. can’t be divided into other elements)

Question 5

How do context free languages work

Answer 5

Context-free languages describe which strings are and are not
possible in a language by laying out production rules

Question 6

What are production rules

Answer 6

A production rule is a statement that allows for one values to be replaced by another valid one e.g a –> aa (a can be replaced by aa)

Question 7

What is a recursive statement in BNF

Answer 7

Where a statement is defined in terms of itself

Question 8

When is recursion used in BNF

Answer 8

It is used as a sort of while loop when you dont know the specific length a value will take

Question 9

What can BNF do that Regex cant

Answer 9

Represent languages that involve recursion

Question 10

What is meant by this symbol:
<>

Answer 10

Represents a syntactic item of the language (basically a data type)

Question 11

What is meant by this symbol:
::=

Answer 11

“Is defined by”

Question 12

What are 2 other ways that BNF can be represented

Answer 12

• Syntax Diagrams 1:1
• Parse Trees