Managing Dynamic User Communities in a Grid of Autonomous Resources by Alfieri, R, Cecchini, R, Ciaschini, V, dell'Agnello, L, Gianoli, A, Spataro, F, Bonnassieux, F, Broadfoot, P, Lowe, G, Cornwall, L, Jensen, J, Kelsey, D, Frohner, Á, Groep, D, de Cerff, W, Steenbakkers, M, Venekamp, G, Kouril, D, McNab, A, Mulmo, O, Silander, M, Hahkala, J, Lörentey, K