Question

a)Define a phrase-structure grammar.

b)What does it mean for a string to be derivable from a string wby a phrase-structure grammar G?

Short answer

1. A phrase structure grammar (V, T, S, and P) represents a language's description; V is the alphabet, T is a collection of terminal symbols, S is the start symbol, and P is a production set.
2. If a string w can be produced from the start symbol S using a series of productions, then the string w can be derived from the phase structure grammar.

Step-by-step solution

Definitions

A collection of pieces that can be used to build strings is called an alphabet.

The set of all possible strings across an alphabet is divided into languages.

Phrase-structure grammar

(a)

The description of a language is represented in a phrase structure grammar by the letters V, T, S, and P, which stand for the alphabet, a set of terminal symbols, a set of start symbols, and a set of production symbols, respectively.

The concept of derivable

(b)

The phase structure grammar can be used to derive a string w if the start symbol S can be used to construct the string through a succession of productions.

Therefore, the require definition of phrase structure grammar.