1. Allen, J.F.: Maintaining knowledge about temporal intervals. Commun. ACM 26, 832–843 (1983)
2. Atanassov, K.T.: Intuitionistic fuzzy sets. Fuzzy Sets and Systems 20, 87–96 (1986)
3. De Caluwe, R., Van der Cruyssen, B., De Tré, G., Devos, F., Maesfranckx, P.: Fuzzy time indications in natural languages interfaces, pp. 163–185. Kluwer Academic Publishers, Norwell (1997)
4. De Tré, G., De Caluwe, R., Van der Cruyssen, B.: Dealing with time in fuzzy and uncertain object-oriented database models. In: EUFIT 1997, 1157–1161 (September 1997)
5. Lecture Notes in Computer Science;G. Tré De,2009