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 International Conference on Complex Systems (ICCS2007)

An Overview of Scale Hierarchy in Complex-Adaptive Systems

Gary Nelson
Homeland Security Institute

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     Last modified: August 31, 2007

Scale hierarchy theory has been articulated by Stan Salthe primarily in a biological context of physical size and rates of change. Gary Nelson has applied Salthe’s theory to the “logical” domain of information-generating agents coordinated in a risk-managing enterprise. In both physical and logical domains then, scale hierarchy is a powerful framework for the interpretation of self-organizing (evolutionary) systems. The theory can also be applied prescriptively to purposeful enterprises where conventional planning paradigms for development are thwarted by uncertainty (risk). Scale hierarchy encompasses these qualitatively different domains of evolution and development because it includes the triadic relation of mechanism, the interaction of loosely-coupled mechanisms, and the emergence of higher level organizations (systems) of mechanisms. By linking causality and emergence, scale hierarchy provides useful interpretations of Peircean first/second/thirdness and Aristotelian causes while refuting the easy dichotomy between network and hierarchy. This powerful theory can claim to be an architecture of the structure and dynamics of all evolutionary development (including self-organizing or complex-adaptive system), and further leads to quantification, by enumeration of scale levels, of what is meant by “system of systems”. The paper gives an overview of scale hierarchy theory that is intended to reveal its relevance to and unification of many aspects of complexity.

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