This paper presents the ARS (Actor-Role-Signature) model designed to easily manage open groups with fluid boundaries in dynamic and rapid changing environment. This work is part of the ELeGI "European Learning Grid infrastructure" project. Using the grid for e-learning can be considered as a major innovation that will boost Internet potential for group collaborative work. The addressed problem is to define a model of MAS to support a new on-line process, the e-Qualification (e-learning qualification), in order to assess both formal and informal learning in virtual learning communities. Agents working in Peer-to- Peer mode, will handle user's e-Portfolios as knowledge prosthesis and exploit e-Qualification processes as aggregation methods to dynamically gather users in working groups, and qualify their knowledge after a training session.