Define Product process problem in experimental design method

In food product design, there are two different kinds of system problems - process and mixture problems - that should be dealt with by different statistical experimental methodologies.
 
In the process problem, all the independent variables are not related to each other but are orthogonal to each other. The change of one variable is not restricted by another  variable. Geometrically, the lines representing these variables meet at right angles. In bread making for example, the temperature of the baking oven can, in principle, be chosen without any influence on the setting  of baking time. Of course, only suitable settings of oven temperature and baking time can lead to desired bread baking results. To solve a process problem, the statistical experimental designs used should contain no or few correlations between the independent variables, so that their natural or original properties of "independence" can be retained.  These kinds of statistical experimental designs are usually factorial experimental designs or designs derived from it.