This paper by D.L. Parnas discusses the criteria for modularizing systems to enhance flexibility, comprehensibility, and development efficiency. It presents a conventional and an unconventional decomposition of a KWIC index production system, highlighting the advantages of the unconventional approach. The conventional decomposition divides the system into modules based on processing steps, while the unconventional one uses "information hiding" as a criterion, where each module hides specific design decisions from others. The paper emphasizes that the order of processing steps should not be the primary basis for decomposition, and that modules should be designed to hide design decisions. It also discusses the benefits of hierarchical structure and the importance of maintaining multiple representations of the program for different purposes. The conclusion suggests that starting with a list of difficult or changeable design decisions is more effective than using flowcharts for modularization.This paper by D.L. Parnas discusses the criteria for modularizing systems to enhance flexibility, comprehensibility, and development efficiency. It presents a conventional and an unconventional decomposition of a KWIC index production system, highlighting the advantages of the unconventional approach. The conventional decomposition divides the system into modules based on processing steps, while the unconventional one uses "information hiding" as a criterion, where each module hides specific design decisions from others. The paper emphasizes that the order of processing steps should not be the primary basis for decomposition, and that modules should be designed to hide design decisions. It also discusses the benefits of hierarchical structure and the importance of maintaining multiple representations of the program for different purposes. The conclusion suggests that starting with a list of difficult or changeable design decisions is more effective than using flowcharts for modularization.