Context Sensitive Grammars & Unrestricted Grammars

• Unrestricted Grammars are the largest family of grammars in the Chomsky hierarchy. The languages described by them are the recursively enumerable languages (r.e. languages).
• Unrestricted grammars have production rules of the form: a -> b, which a and b arbitrary strings of grammar symbols.
• Context Sensitive Grammars are a subset, with the additional rule that of production rules a -> b, the length of b has to be at least the length of a. Context Sensitive Grammars describe Context Sensitive Languages.
• Almost all concievable languages are Context Sensitive Languages.
• Recursively enumerable languages require a Turing Machine to parse, while Context Sensitive Languages can be parsed with a Linear Bounded Automaton; a Turing Machine with a finite amount of tape.