http://www.nltk.org/book/ch00.html
After this, the pace picks up, and we move on to a series of chapters covering fundamental topics in language processing: tagging, classification, and information extraction (Chapters 5-7). The next three chapters look at ways to parse a sentence, recognize its syntactic structure, and construct representations of meaning (Chapters 8-10). The final chapter is devoted to linguistic data and how it can be managed effectively (Chapter 11). The book concludes with an Afterword, briefly discussing the past and future of the field.