J. Hartmann, M. Vieira, and A. Ruder. Proceedings of the International Workshop on Software Product Line Testing (SPLiT 2004), page 58--65. Boston, MA, (August 2004)
A. Braganca, and R. Machado. SPLC '07: Proceedings of the 11th International Software Product Line Conference, page 3--12. Washington, DC, USA, IEEE Computer Society, (2007)