P. Baxendale, Machine-made index for technical literature -- an experiment, in IBM Journal, pages 354-361, October 1958. 

Christopher Culy, An extension of phrase structure rules and its application to natural language. Master's thesis, Stanford University, 1983. 

DESY, The High Energy Physics Index keywords, http://www-library.desy.de/schlagw2.html 

CERN. DH group, ETT division. The CERN Document Server.http://cds.cern.ch/ 

Oak Ridge, Gail Hodge, CENDI agency indexing system descriptions: A baseline report, Technical report, CENDI, 1998 http://www.dtic.mil/cendi/publications/98-2index.html 

Paul Ginsparg, arXiv.org e-print archive, http://www.arxiv.org/ 

INIS thesaurus, http://www.iaea.or.at/worldatom/publications/inis/inis.html 

INSPEC thesaurus, http://www.iee.org.uk/publish/inspec/ 

H. Luhn, A statistical approach to mechanized encoding and searching of literary information, in IBM Journal of Research and Development 1 (4) 309-317, 1957. 

Daniel Marcu, Discourse trees are good indicators of importance in text, Technical report, Information Science Institute, University of Southern California, 1997. 

I.C McIlwaine, The Universal Decimal Classification - a guide to its use, Technical report, UDC Consortium. 

D. Dallman; J. Y. Le Meur, Automatic keywording of high energy physics, In 4th International Conference on Grey Literature : New Frontiers in Grey Literature, Washington, DC, USA, Oct. 1999. 

National Library of Medicine, Bethesda, US. Medical Subject Headings (MeSH), 1993. 

American Institute of Physics, Physics and Astronomy Classification Scheme http://publish.aps.org/PACS/ 

A. M. Robertson and P. Willett, Evaluation of techniques for the conflation of modern and seventeenth century english spelling, in Tony McEnery and Chris Paice, editors, Proceedings of the BCS 14th Information Retrieval Colloquium, Workshops in Computing, pages 155-168, London, April 13-14 1993. Springer Verlag. 

Gerard Salton, Automatic text analysis, Technical Report TR69-36, Cornell University, Computer Science Department, June 1969. 

Ralf Steinberger, Cross-lingual keyword assignment, in L. Alfonso Ureña López, editor, Proceedings of the XVII Conference of the Spanish Society for Natural Language Processing (SEPLN 2001), pages 273-280, Jain (Spain), September 2001. 

C. J. van Rijsbergen, Information Retrieval. London: Butterworths, 1975 http://www.dcs.gla.ac.uk/Keith/Preface.html 

Natasha Vieduts-Stokolo, Concept recognition in an automatic text-processing system for the life sciences, 1987.