More than the sum of its members

Systems that recommend items to a group of two or more users raise a number of challenging issues that are so far only partly understood. This paper identifies four of these issues and points out that they have been dealt with to only a limited extent in the group recommender systems that have been developed so far. The issues are especially important in settings where group members specify their preferences explicitly and where they are not able to engage in face-to-face interaction. We illustrate some of the solutions discussed with reference to the TRAVEL DECISION FORUM prototype. The issues concern (a) the design of suitable preference elicitation and aggregation methods, in particular nonmanipulable aggregation mechanisms; and (b) ways of making members aware of each other's preferences and motivational orientations, such as the use of animated representatives of group members.