There are three qualitative attributes—flexibility, accessibility and maintenance. They are referred to as C4, C5 and C6, respectively, hereafter. Flexibility involves two aspects: the first is the capability to perform a variety of tasks under a variety of operating conditions; second is the flexibility of future expansion. Accessibility involves material handing and operator paths. Finally, the maintenance issue involves the required space for maintenance engineers and tool movement. The qualitative attributes are evaluated using an analytic hierarchy process (AHP). Readers are referred to Yang and Kuo [10] for details of the AHP evaluation process, as well as the block layout figures of the 17 design alternatives. The performance ratings for the 18 alternatives with respect to the six attributes are summarized in Table 2: decision matrix.