“…AL techniques have been used to economically learn robot policies [21,22,55,62] and task representations [25,34,41,53], to guide efficient information gathering [17], and to learn reward functions by querying the user with different type of queries [9,10,24,59]. Another line of research has instead concentrated on the interactive nature of AL, with work investigating the design of active robot learners [18,19], the ability of users to answer the robot's questions [32,57] and the development of AL strategies that take into account the user in their query selection [11,38,54]. New types of queries, different from asking for a positive or negative label, have been adopted or developed through this line of research, including demonstration queries [16,19], feature queries [10,16,19], and comparison queries [12,59].…”