 In practical decision making, there are often several preference relations that have to be taken into account. The different preference relations represent different aspects of the subject matter concerned by the decision. For instance, when choosing among alternative architectural designs for a new building, we will have a whole set of aspects, each of which can be expressed with a preference relation: costs, sustainability, aesthetics, fire safety etc. In other cases, the various preference relations represent the wishes or interests of different persons. This applies for instance when a group of people with different preferences plan a joint vacation trip. 