Organisations increasingly have to deal with complex problems. They often use multidisciplinary teams to cope with such problems where different team members have different perspectives on the problem, different individual knowledge and skills, and different approaches on how to solve the problem. In order to solve those problems, team members have to share their existing knowledge and construct new knowledge. Theory suggests that negotiation of common ground can positively affect team decision making on the solution of complex problems, by facilitating knowledge sharing across perspectives. In a small scale study with student groups, external representations supported by a specific negotiation ontology were used to facilitate negotiation by encouraging participants to make their beliefs and values explicit. Results showed that the external representations supported clarifying contributions to group members and increased group participation in discussions.