@article{j:idf,
	title = {A Statistical Interpretation of Term Specificity and its Application
  in Retrieval},
	author = {Karen {Sparck Jones}},
	journal = {Journal of Documentation},
	number = {1},
	pages = {11--21},
	volume = {28},
	year = {1972},
	biburl = {http://www.bibsonomy.org/bibtex/256383537fc8baccc6b6d687e028485e4/nlp},
	keywords = {2000 book nlp }
}