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Part A Theoretical Framework This section of the book focuses on the connotations of urban metabolism research and its associated areas of research�� the basic theory�� and the resulting theoretical framework for this research. Using the CiteSpace literature analysis tool�� I mined the literature to define the knowledge structure�� context�� and evolution of urban metabolism research. By so doing�� I was able to comprehensively summarize the subject��s background�� key insights from related fields�� and the foundation for urban metabolism research. On this basis�� I describe the importance of the study of urban metabolism and establish a technical framework and research paradigm for the research based on the theories of urban complex ecosystems�� thermodynamics�� and systems ecology. In subsequent chapters�� I will demonstrate how this framework supports real-world studies of urban ecosystems and management of these ecosystems to improve their sustainability. Chapter 1 Connotations of Urban Metabolism 1.1 The concept of an urban organism and ecosystem To benefit from the analogies with ecosystems and organisms�� which have been rigorously studied by researchers�� it is first necessary to understand the relationship between the two. On the one hand�� a city resembles an ecosystem because it is composed of multiple components (e.g.�� sectors such as the manufacturing industry and agriculture) that resemble living organisms because they exchange materials�� energy�� and information both with each other and with their environment. Ecosystems don��t really have a metabolism�� but do have flows of materials and energy that resemble the metabolic flows in an organism. On the other hand�� cities are not living bodies with a beating heart�� bones�� muscles�� and nerves�� and they don��t have a simple metabolism that provides materials and energy to different parts of the body. The purpose of comparing cities with ecosystems and organisms is to use familiar terminology that makes it easier to understand the complex flows within an urban ecosystem or organism (i.e.�� its metabolism). In this chapter�� I will review how the organism metaphor has been applied to the formation and development of cities�� and will explore the similarities between cities and living organisms in terms of their structure and functions. Chengshi is the Chinese word for a city. It is composed of two parts: cheng refers to a defensive area surrounded by walls and a moat�� and shi refers to a center for the distribution of materials�� energy�� information�� capital�� and people�� as well as a place where trade occurs (i.e.�� a market). Cities were originally centers of agriculture. Subsequently�� three new social divisions evolved (animal husbandry�� manufacturing of specialized products�� and commerce) and cities became increasingly complex. As human society evolved and became increasingly complex�� the ability of humans to exploit nature increased�� providing an incentive to concentrate on activities such as animal husbandry and agriculture in a defined area to improve labor productivity�� leading to the development of early small settlements that became the embryo for a market. At the same time�� the exchange of goods between groups of people (e.g.�� professions such as herding and crop cultivation) created the material conditions for private ownership. As society continued to evolve�� the use and improvement of metal tools led to the evolution of craftsmanship and a form of manufacturing industry that was distinct from agriculture. The efficiency permitted by this separation led to the rapid development of commodity production�� an increasingly obvious gap between the rich and the poor�� and the emergence of settlements dominated by the crafts and by a manufacturing industry. This�� in turn led to the continuous growth and development of markets�� which function as areas in which exchanges of materials�� energy�� and information occur. These markets were supported by the emergence of merchants who specialized in trading of various commodities�� accompanied by the separation of mental and physical labor. As some merchants grew rich�� the continuous accumulation of commercial capital led to continuing maturation of the market. However�� the emergence of private ownership led to conflict between early rulers or governments and private owners over which group should control resources. To increase their wealth�� some settlements or merchants provoked conflict with others�� leading to a need to create a city with walls and a moat to protect its market (i.e.�� chengshi). This represents an early example of the concept of an organism (the city) that is clearly separated from its external environment. Cities usually developed in areas with suitable natural conditions�� such as alluvial plains near bodies of water. By taking advantage of steadily evolving social structures and technologies�� cities allowed humans to exploit natural resources more efficiently�� thereby al