Hesitant fuzzy linguistic term sets for linguistic decision making: Current developments, issues and challenges

The fuzzy linguistic approach is frequently considered as a solution for qualitative decision making. In the traditional framework of linguistic decision making, the representation of linguistic information is quite limited because the information has to be expressed by one predefined term. Hesitant fuzzy linguistic term sets (HFLTSs), which can be elicited by comparative linguistic expressions, have been proposed recently for the convenience of utilizing several consecutive terms at the same time and accommodating uncertainties and hesitations in human linguistic assessments. Since it was introduced, a large number of publications have been devoted to developing the theories, methods and applications of HFLTSs. In this paper, the concept and characteristics of HFLTSs are revisited at first and then the recent developments are reviewed and classified according to their computational strategies. Based on which, a comparative analysis of some similar techniques is presented to recognize the role of HFLTSs in linguistic decision making. Finally, some existing issues and current challenges are summarized to guide the prospective research of HFLTSs towards a high-quality progress.