Defining context-free grammar

Now let's focus on NLU, and to understand it, first we need to understand context-free grammar (CFG) and how it is used in NLU.

Context-free grammar is defined by its four main components. Those four components are shown in this symbolic representation of CFG:

• A set of non-terminal symbols, N
• A set of terminal symbols, T
• A start symbol, S, which is a non-terminal symbol
• A set of rules called productionrules P, for generating sentences

Let's take an example to get better understanding of the context-free grammar terminology:

X ->

Here, X->

is called the phrase structure rule or production rule, P. X ε N means X belongs to non-terminal symbol;

ε {N or T} means

belongs to either terminal symbols or non-terminal symbols. X can be rewritten in the form of

. The rule tells you which element can be rewritten to generate a sentence, and what the order of the elements will be as well.

Now I will take a real NLP example. I'm going to generate a sentence using CFG rules...