1. CST229 Week 6 Questions or concerns? Homework #4 due
Hand back Homework #3
Reading: Chapters 12&13
Quick note about Lab#1
Lab#1 due tomorrow at midnight via
Revised course schedule
Quick look at Chapter 12
Test#1

2. Three main topics Languages Machines Grammar
Notations for defining the language
Set notation
Recursive definitions
Regular expressions (for a specific type of language – regular languages)
Definitions serve as a recognizer or a generator
Machines
Recognizer – given a definition and a string, the machine can tell if the string is in the language
Finite Automata - Deterministic Finite Automata (ch. 5)
Nondeterministic Finite Automata (ch. 7) – optional
Grammar
Just another notation for defining languages.
Unlike regular expressions which only define regular languages, grammar is more flexible and more general.

3. Grammar
Language Hierarchy (Noam Chomsky) based on complexity of structure
Regular – no nesting
Context-Free – handles nesting structures. Syntax only, no meaning
Context-Sensitive – adds semantic information
Recursive enumerable – more complex, closer to natural languages

4. Recursive Enumerable
Context-sensitive
Context-Free
Regular languages

5. Grammar
Two different notations, developed independent of each other, but very similar
Chomsky
Backus / Naur (John Backus / Peter Naur) Form
Notation for defining languages, particularly programming languages.
Recursive by nature (similar to recursive definitions)
Nondeterministic by nature
We use grammar as a recognizer/generator just like other language definitions

6. Grammar Let’s start with a recursive definition
Lp = string over {a,b} where w = wr
Base:  is in Lp, so is a & b
Rec: if x is in Lp, then so is axa and bxb

7. Grammar Another notation S ->  S -> a S -> b S -> aSa
S -> bSb