9.7: Chomsky Hierarchy

Turing Machine

Turing Machine (II) Unrestricted grammar Recognized by Turing machine It consists of a read-write head that can be positioned anywhere along an infinite tape. It is not a useful class of language for compiler design.

Linear-Bounded Automata

Linear-Bounded Automata Context-sensitive Restrictions Left-hand of each production must have at least one nonterminal in it Right-hand side must not have fewer symbols than the left There can be no empty productions (N)

Push-Down Automata

Push-Down Automata (II) Context-free Recognized by push-down automata Can only read its input tape but has a stack that can grow to arbitrary depth where it can save information An automation with a read-only tape and two independent stacks is equivalent to a Turing machine. It allows at most a single nonterminal (and no terminal) on the left-hand side of each production.

Finite-State Automata

Finite State Automata (II) Regular language Anything that must be remembered about the context of a symbol on the input tape must be preserved in the state of the machine. It allows only one symbol (a nonterminal) on the left-hand, and only one or two symbols on the right.