17. The processing device of claim 1 , wherein the at least one boolean operator includes at least one from among AND operator (AND co-occurrence frequency), and OR operator (OR co-occurrence frequency).
17. The processing device of claim 1 , wherein the at least one boolean operator includes at least one from among AND operator (AND co-occurrence frequency), and OR operator (OR co-occurrence frequency). 19. The processing device of claim 17 , wherein: first candidate condition is satisfied if the OR co-occurrence frequency acquired for an immediately lower category is lower than the OR co-occurrence frequencies acquired for the category of interest and categories above the category of interest excluding the topmost one with reference to a given comparison criterion, the distribution of the OR co-occurrence frequencies of the on-the-path categories is in conformity with the given distribution pattern associated with the first candidate condition.