The scenario planning approach of Fritz Zwickey (see http://www.swemorph.com/pdf/gma.pdf ) is worth considering. In his approach, you start with the objective/goal/output and work backwards towards its “atomic” components (attributes). By fleshing out full sets of attributes, you can then move forward and develop possible, alternative objectives/goals/outputs based on fuller sets of attributes. (see http://www.mindtools.com/pages/article/newCT_03.htm ).