1. Salton G., and McGill M.J.: Introduction to modem information retrieval. McGraw-Hill Int. Book Co (1984).
2. Bosc P., Dubois, D., Pivert, O., Prade H.: Fuzzy division for regular relational databases, 4th Int. IEEE Conference on Fuzzy Systems (FUZZ-IEEE /IFES’95), Yokohama (Japan), March 1995, (1995) 729–734.
3. Bosc P.: Some views of the division of fuzzy relations, 5th International Workshop on Current Issues on Fuzzy Technologies (CIP7 95), Trento (Italy), June 1995, (1995) 14–22
4. Bosc P., and Pivert O.: Some approaches for relational databases flexible querying. J. oflntelligent Information Systems 1, (1992) 323–354.
5. Sparck-Jones K.A.: A statistical interpretation of term specificity and its application in retrieval. J. of Documentation 28 (1) (1972) 11–20.