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Unformatted text preview: IEEE TRANSACTIONS ON SYSTEMS, MAN, AND CYBERNETICSPART A: SYSTEMS AND HUMANS, VOL. 40, NO. 4, JULY 2010 839 Contrasting Views of Complexity and Their Implications For Network-Centric Infrastructures David L. Alderson, Member, IEEE , and John C. Doyle Abstract There exists a widely recognized need to better un- derstand and manage complex systems of systems, ranging from biology, ecology, and medicine to network-centric technologies. This is motivating the search for universal laws of highly evolved systems and driving demand for new mathematics and methods that are consistent, integrative, and predictive. However, the the- oretical frameworks available today are not merely fragmented but sometimes contradictory and incompatible. We argue that complexity arises in highly evolved biological and technological systems primarily to provide mechanisms to create robustness. However, this complexity itself can be a source of new fragility, leading to robust yet fragile tradeoffs in system design. We focus on the role of robustness and architecture in networked infrastructures, and we highlight recent advances in the theory of distributed control driven by network technologies. This view of complexity in highly organized technological and biological sys- tems is fundamentally different from the dominant perspective in the mainstream sciences, which downplays function, constraints, and tradeoffs, and tends to minimize the role of organization and design. Index Terms Architecture, complexity theory, networks, opti- mal control, optimization methods, protocols. I. INTRODUCTION M ANY cyber-technical visions convincingly suggest that net-centric technology will provide unprecedented lev- els of capability and efficiency to support the operation and management of modern societys most vital functionsranging from delivery of economic goods and services, business processes, global financial markets, education, health care, defense, and other government services . A fundamental challenge is to understand and manage the growing complexity of these systems . Historically, we have done a poor job in managing the fragili- ties created by our complex networks, from global warming to ecosystem destruction, global financial crises, etc. In many cases, past failures are due to fragilities that were direct side effects of mechanisms that promised to provide great benefits, including robustness. Thus, robust yet fragile (RYF) is an increasingly central issue in network-centric infrastructures and Manuscript received July 1, 2008; revised March 10, 2009. Date of publication June 3, 2010; date of current version June 16, 2010. This paper was presented in part at the 2007 IEEE International Conference on Systems, Man and Cybernetics, Montreal, QC, Canada, October 710, 2007. This work was supported by the Office of Naval Research under MURI Awards 0001408WR20242 and N000140810747. This paper was recommended by Associate Editor M. Ulieru.Associate Editor M....
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