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Conlusions of Watchmakers' parable

This simple story reveals that the ability to develop large complex systems depends on two elements in fundamental and universal ways. The first element is the environment. How frequently and how seriously will the environment disturb the developer? Typical disturbances in the CIM/E domain are: The contemporary manufacturing environment increasingly provides these disturbances. The second element is the ability to develop stable subsolutions (subassemblies, subsystems) that survive these disturbances. When the environment disturbs development activities more frequently, the need for stable subsolutions increases. For the developers of large com- plex systems, this means that they need modules of appropriate size that permit the rapid development and adaptation of the overall system to the environment. Such systems evolve through the gradual replacement and addition of modules that survive themselves the changes in the environment (when seen individually) much longer than the large system itself (without evolution). A short analysis shows that developers are hitting against the proverbial brick wall. Consider a system with n components. Assume that the probability of surviving the next time slot for these components is p, where p < 1, and that the survival of the components is mostly unrelated. In this case, the probability that the system survives the next time slot is p**n. In other words, the probability of survival for the overall system decreases exponentially with the number of components. Very rapidly, the expected lifetime of the system will drop below the level were it is able to repay its development and maintenance costs when the number of components increases. The parable also reveals that hierarchy comes naturally in large complex systems because it drastically increases the probability of their emergence and survival. In other words, large complex systems invariably have a hierarchical structure. However, this does not mean that it is necessary (or even feasible) to postulate a hierarchy when starting to develop a complex artificial system. To the contrary, it means that a hierarchy will/must emerge that reflects hard con- straints in the environment; it reflects the presence and absence of stable and suitable subsolutions. Postulating a hierarchy up front may cause problems instead of solving problems. Developers must look for possible natural hierarchies. Furthermore, the parable reveals the limitations of orthodox top-down development. When developers follow it in a dogmatic way, the development of subsystems occurs within a well-defined context because of the top-down approach. In combination with economic pressures, subsystem developers will minimise both their effort and the complexity of their subsolutions. Therefore, they design and op- timise subsystems for a specific context. This results in subso- lutions that are unable to survive disturbances from the environment significantly better than the overall system, which makes the emer- gence of large complex systems in demanding environments impossible. Experience confirms this: automated manufacturing systems are either small (for example islands of automation) or enjoy a stable envi- ronment (for example mass production systems). Finally, the parable triggered the events that made Arthur Koestler proposed, some 25 years ago, the word HOLON.

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This file is maintained by Jo.Wyns@mech.kuleuven.ac.be
Created : Aug, 1994
Last update: Jan 5, 1995

URL : http://www.mech.kuleuven.ac.be/pma/project/goa/hsm-int/parab_cl.html