Formal Languages and Compilers
- Course notes onthe definition of formal languages and the use of context free languages in compiler construction.
- http://shekel.jct.ac.il/~rafi/formcomp.pdf#search=%22context%20sensitive%20languages%20compilers%22

Formal Grammars and Languages
- A survey article on formal systems that define families of formal languages arising in many computer science applications with primary focus on context-free languages.
- http://www.cs.ucr.edu/~jiang/cs215/tao-new.pdf#search=%22context%20sensitive%20languages%20compilers%22

Push-Down Automata and Context-Free Grammars
- Lecture notes defining context free grammars and closure and decidability properties of context free languages. There is a short section showing that natural languages are not context free.
- http://people.umass.edu/partee/726_04/lectures/Lecture%2014%20PDAs%20and%20CFGs.pdf#search=%22pushdown%20automata%22

Context-Free Grammars and Parsing
- An article defining the grammar and how Binary Normal Form (BNF) is used to parse words in a context free language. An example shows how operator precedence is preserved in a context free grammar.
- http://eli-project.sourceforge.net/elionline4.4/syntax_1.html

Context-free Grammar
- A Wikipedia article that defines context free grammars and uses them to generate context free languages.
- http://en.wikipedia.org/wiki/Context-free_grammar