To be familiar with the probability variable elements expressed by Equation (2), let us consider for example the statement "quality-assurance aspect is achievable and sustainable for the mould polymerisation process” and we let the letter "x” denotes the property named "quality- assurance aspect is achievable and sustainable” and the subscript "k” refers to the stage number involved in the design process, which corresponds here to "mould polymerisation process”, we can then characterise the above statement as "xk”. For instance, if the subscript k=4, then the statement can be represented as ”x4”. The circular limit line labelled "Q” shown in Figure 3 encompasses the region that contains all the members that have the same property "quality – assurance aspect is achievable and sustainable” (x1, x2, , xm).
Proceeding in the same manner as previously, we may characterise the statement "environment-protection aspect is achievable and sustainable for resin type” as "zk", where the letter "z” denotes the property named "environment-protection aspect is achievable and sustainable” and the subscript "k” denotes the stage number involved in the design process which corresponds here to "resin type”. For instance, if the subscript k=2, then the previous statement will be symbolised as "z2”. The circular limit line called "H” shown in Figure 3 encompasses the region that contains all the members that have the same property "environment-protection aspect is achievable and sustainable” (z1 , z2, zp).
According to this representation for modelling, the property is always symbolised with a letter x, y or z associated to quality, health or environment, respectively. Whereas the stage number involved in the design process is symbolised with a subscript k (k=1,2,…, N). The statement is denoted by "xk”, "yk” or "zk”.
