RESTART

Restart.

Remember?

We were talking about formal languages.

Formally

a formal language is just a set of strings.

OK?

A set?

Not necessarily an internal structure of strings.

They're strings that we're accepting.

And that's mathematically relatively satisfying.

But computationally, it's not.

And so we started looking at what's

called phrase structure grammars, or just grammars.

And remember

a grammar basically has four components.

One is we have non-terminal symbols.

Think of those as the grammatical categories.

If you have a word grammar of English,

then noun phrases and nouns and verbs and so on

would be the non-terminals.

And we have a set of terminal symbols.

Those would be the words of English,

or the sentences of English, or something like this.

And very importantly, we have a set of production rules.

Production rules is just you can rewrite something

like a noun phrase to the word the dog

or something like that.

OK?

And the last component is we have a start symbol.

That is basically, if we start with a start symbol,

usually something like sentence or so,

or program for grammars for programming languages.

If you can rewrite, if you can find

a string of applications of productions rule

that ends in a terminal string, then we

say the grammar accepts this.

Yes?

In the terminal string, how are the strings represented?

They are in a double quote or a single quote?

How do we know that the death of the string

or the death of the word of the string?

It's just a sequence of symbols by definition.

And a sequence of symbols as terminal

if it doesn't have any non-terminal symbols in it.

Any sequence of symbols

anything

that is set for terminal?

Like if we have the terminal state of a term,

if all the four symbols will be terminal state of only one