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Network Science Executive Summary Society depends on a diversity of complex networks for its very existence. In the physical sphere, these include the air transportation network, highways, railroads, the global shipping network, power grids, water distribution networks, supply networks, global financial networks, telephone systems, and the Internet. In the biological arena, they include genetic expression networks, metabolic networks, our bodies, ant colonies, herds, food webs, river basins, and the global ecological web of Earth itself. In the social domain, they include governments, businesses, universities, social clubs, churches, public and private school systems, and military organizations. The military’s dependence on interacting networks in the physical, information, cognitive, and social domains is clear from its effort to transform itself into a force capable of network-centric operations (NCO). In spite of society’s profound dependence on networks, fundamental knowledge about them is primitive. Many physical networks—for example, global communication and transportation networks—have quite advanced technological implementations, but their behavior under stress still cannot be predicted reliably. For biological and social networks, scientists do not understand what they are, much less how they operate. There is a huge gap between what we need to know about networks to ensure the smooth working of society and the primitive state of our fundamental knowledge. This gap makes the military vision of NCO problematic, at best. STUDY APPROACH The present study was commissioned by the Army to find out whether identifying and funding a new field of investigation, “network science,” could help close this gap. The chair worked with the NRC staff to nominate committee members representative of the broad scope of efforts in network research and also of the interests in this topic on the part of the Army. At its initial meetings the committee focused on data collection tasks. Members were invited to present their ideas about the definition and content of network science. This exercise was expanded to encompass telephone interviews with a number of distinguished researchers and a questionnaire distributed inquiring about the role of networks in today’s global economy and the military in particular. The committee also collected data on the use of networks in the military, learning from extensive reading and presentations at its second and third meetings. The results of these data-gathering tasks are reported in Chapters 2 through 4. The committee formed two special task teams. One team surveyed academic courses on network research to determine the content of core knowledge about networks. The results of this effort are reported in Chapter 5 based on the data presented in Appendix C. The other task team developed and circulated the questionnaire to as broad a cross section of the network research community as possible given the time and financial constraints of this study. The committee’s analysis of the responses is reported in Chapter 6 and Appendix D. After characterizing the importance and content of network science, the committee turned its attention to the matter of how the Army might create value by investing in research on networks. This task was complicated by the fact that “the Army” is shorthand for a diverse group of constituencies with multiple agendas and priorities. The committee formed into new task teams to formulate three different investment scenarios that span the various interests and agendas. The scenarios are reported in Appendix E and are summarized, along with specific findings, in Chapter 7. Representative literature used over the course of the study is listed in Appendix F. The body of the report—Chapters 2 through 7 and Appendixes C through E—contains the factual findings, and Chapter 8 contains the committee’s conclusions and recommendations. Box ES-1 provides a summary of how the various report chapters respond to the statement of task.
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Network Science BOX ES-1 Summary of Responses to the Statement of Task The Assistant Secretary of the Army (Acquisition, Logistics, and Technology) has requested the National Research Council (NRC) Board on Army Science and Technology (BAST) conduct a study to define the field of Network Science. The NRC will: Determine whether initiation of a new field of investigation called Network Science would be appropriate to advance knowledge of complex systems and processes that exhibit network behaviors. If yes, how should it be defined? A working definition of network science is the study of network representations of physical, biological, and social phenomena leading to predictive models of these phenomena. Initiation of a field of network science would be appropriate to provide a body of rigorous results that would improve the predictability of the engineering design of complex networks and also speed up basic research in a variety of applications areas (Chapter 4). Identify the fields that should comprise Network Science. What are the key research challenges necessary to enable progress in Network Science? General consensus exists among practitioners of network research in diverse application areas on topics that constitute network science (Chapter 5). There are seven major research challenges (Chapter 6). Identify specific research issues and the theoretical, experimental, and practical challenges to advance the field of Network Science. Consider such things as facilities and equipment that might be needed. Determine investment priority, time frame for realization, and degree of commercial interest. Current military concepts of “net-centricity” are based on applications of computer and information technology that are far removed from likely results of basic research in network science. Table ES-1 lists current areas of network research of interest to the Army, including priority, time frames, and commercial interest (Chapter 3). Current funding policies and priorities are unlikely to provide adequate fundamental knowledge about large complex networks that will advance network-centric operations. Besides the information domain, there are social, cognitive, and physical technology domains in the current conceptual framework for network-centric operations; there is no “biological” domain (Chapters 2–4). A basis for network science is perceived in different ways by the communities concerned with engineered, biological, and social networks at all levels of complexity. Basic research efforts are incoherent (Chapters 5 and 6). Options for obtaining value from investments in network science include scenarios ranging from building a base of basic research, to leveraging business practices for market-driven R&D in specific areas of network applications, to creating a robust capability for network-centric operations (Chapter 7). Given limited resources (and likely investments of others), recommend those relevant research areas that the Army should invest in to enable progress toward achieving Network-Centric Warfare capabilities. Recommendations 1, 1a through 1d, 2, and 3 provide the Army with an actionable menu of alternatives that span the opportunities accessible to it. By selecting and implementing appropriate items from this menu, the Army can develop a robust network science to enable the desired progress (Chapter 8). NOTE: The statement of task is in lightface; the summary of responses is in boldface. OVERARCHING CONCLUSIONS The committee reached three overarching conclusions about the significance of networks and the state of knowledge about them. First, it documented the pervasive influence of networks in all aspects of life—biological, physical, and social—and concluded that they are indispensable to the workings of the global economy and to the defense of the United States against both conventional military threats and the threat of terrorism. Second, the fundamental knowledge needed to predict the properties of large infrastructure networks (such as the Internet and power grid) and vital social networks (the global economic system and military command and control) is
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Network Science primitive. Not even physical communications networks can be designed so that their resistance to failure and scaling up from small to large can be predicted a priori with confidence. Networks are built on top of one another. Social networks, for example, are built on information networks, which in turn are built on communications networks that operate using physical networks for connectivity. The networks required to make NCO for the military a reality span the physical, information, cognitive, and social domains. They are interactive and mutually interdependent. There is no science today that offers the fundamental knowledge necessary to design large, complex networks in such a way that their behaviors can be predicted prior to building them. Given this shortfall, trying to implement network-centric operations capabilities as envisioned by the Department of Defense (DOD) is like trying to design and build a modern combat jet aircraft without resorting to the science of fluid dynamics. Third, in spite of the need for a science of networks and the high level of interest in the scientific community, current funding policies and practices of federal agencies are focused on specific network applications and are not focused on accumulating fundamental knowledge about networks. Research on networks is fragmented. It is supported in disciplinary stovepipes that encourage jargon, parochial terms, and local values. Fundamentals of network structure, dynamics, and simulation are being rediscovered by different groups that emphasize uniqueness rather than a common intellectual heritage and methodologies. The fragmentation is aggravated by funding-agency policies and procedures that reward narrow disciplinary interests rather than results that are demonstrably usable for addressing national problems. Nor is funding focused in areas with widespread application, such as the development of predictive models of social networks, which could directly impact vital national problems, from secondary education in urban slums to military command and control. Although researchers, especially the best researchers, are reacting rationally to the incentives placed before them, these incentives reflect poorly the national interests of the United States in a globally connected world. SPECIFIC CONCLUSIONS On the basis of its data collection and analysis, the committee offers the following conclusions containing answers to the specific questions posed in the statement of task. Different research communities give different answers to the question, What is network science? Nevertheless, the committee discerned some basic features. First, network science is distinct from both network technology and network research: It is characterized by the discovery mode of science rather than the invention mode of technology and engineering. Network research encompasses both. Network science is broad in scope, encompassing physical, biological, and social networks. Synergies between network representations and models in these domains give it power. It creates fundamental knowledge that enables the a priori prediction of the behaviors of diverse networks in contrast to their a posteriori characterization. In short, network science consists of the study of network representations of physical, biological, and social phenomena, leading to predictive models of these phenomena. The remarkable diversity and pervasiveness of network representations and models render network science a topic that can be leveraged by both civil society and the military. A provisional consensus exists around its core contents, making network science an identifiable area of investigation. Excellent research problems on a variety of topics exist. By making an investment in network science, the Army could forge a single approach to a diverse collection of applications. The committee therefore concludes that network science is an emerging field of investigation whose support would address important societal problems, including the Army’s pursuit of NCO capabilities. Although the boundaries of network science are fuzzy, the committee found broad consensus among practitioners in network applications—including physical, biological, social, and information networks—on the key topics, the types of tools that must be developed, and the research challenges that should be investigated. Based on the responses to its questionnaire and its own knowledge, the committee concluded that there are seven major research challenges, the surmounting of which will enable progress in network science: Dynamics, spatial location, and information propagation in networks. Better understanding of the relationship between the architecture of a network and its function is needed. Modeling and analysis of very large networks. Tools, abstractions, and approximations are needed that allow reasoning about large-scale networks, as well as techniques for modeling networks characterized by noisy and incomplete data. Design and synthesis of networks. Techniques are needed to design or modify a network to obtain desired properties. Increasing the level of rigor and mathematical structure. Many of the respondents to the questionnaire felt that the current state of the art in network science did not have an appropriately rigorous mathematical basis. Abstracting common concepts across fields. The disparate disciplines need common concepts defined across network science. Better experiments and measurements of network structure. Current data sets on large-scale networks tend to be sparse, and tools for investigating their structure and function are limited. Robustness and security of networks. Finally, there is a clear need to better understand and design networked
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Network Science systems that are both robust to variations in the components (including localized failures) and secure against hostile intent. Finally, although all the military services have a vision of the future in which engineered communications networks play a fundamental role, there is no methodology for ensuring that these networks are scalable, reliable, robust, and secure. Of particular importance is the ability to design networks whose behaviors are predictable in their intended domains of applications. This also is true in the commercial sphere. The committee therefore concluded that the high value attached to the efficient and failure-free operation of global engineered networks makes their design, scaling, and operation a national priority. The ultimate value derived from these engineered networks depends on the effectiveness with which humans use them. These uses can be beneficial (e.g., better combat effectiveness) or detrimental (e.g., their exploitation by criminal and terrorist groups). Therefore research into the interaction of social and engineered networks is also a national priority. RECOMMENDATIONS The statement of task asks the committee to recommend investments the Army should make in network science. The impact of networks on society transcends their impact on military applications, although both are vital aspects of the total picture. The current state of knowledge about networks is insufficient to support the design and operation of complex global networks for military, political, and economic applications. Advances in network science are therefore essential for developing adequate knowledge for these applications. Recommendation 1. The federal government should initiate a focused program of research and development to close the gap between currently available knowledge about networks and the knowledge required to characterize and sustain the complex global networks on which the well-being of the United States has come to depend. This recommendation is buttressed by increasing evidence that disruptive social networks (e.g., terrorists, criminals) learn to exploit evolving infrastructure networks (e.g., communications or transportation) in ways that the creators of these networks did not anticipate. The global war on terrorism, which is a main driver of military transformation, is only one recent manifestation of this general pattern. Addressing problems resulting from the interaction of social and engineered networks is an example of a compelling national issue that transcends the transformation of the military and that is largely untouched by current research on networks. Within this broad context, recommendations 1a, 1b, and 1c provide the Army with three options: Recommendation 1a. The Army, in coordination with other federal agencies, should underwrite a broad network research initiative that includes substantial resources for both military and nonmilitary applications that would address military, economic, criminal, and terrorist threats. The Army can lead the country in creating a base of network science knowledge that can support applications for both the Army and the country at large. Maximum impact could be obtained by a coordinated effort across a variety of federal agencies, including DOD and the Department of Homeland Security, to create a national program of R&D focused on network science to develop applications that support not only network-centric operations but also countermeasures against international terrorist and criminal threats. Alternatively, if the Army is restricted to working just with the DOD, it should initiate a focused program to create NCO capabilities across all the services. Recommendation 1b. If the Army wants to exploit fully applications in the information domain for military operations in a reasonable time frame and at an affordable cost, it should champion the initiation of a high-priority, focused DOD effort to create a realizable vision of the associated capabilities and to lay out a trajectory for its realization. Finally, if the Army elects to apply the insight from the committee primarily to its own operations, then it can still provide leadership in network science research. Recommendation 1c. The Army should support an aggressive program of both basic and applied research to improve its NCO capabilities. Specific areas of research of interest to the Army are shown in Table ES-1. This table expresses the committee’s assessment of the relative priorities for these areas, the time frames in which one might reasonably expect them to be consummated as actionable technology investment options, and the degree of commercial interest in exploiting promising options. The committee notes that both trained personnel and promising research problems exist in many of these areas, so that the Army should be able to create productive programs readily. Regardless of which options are adopted, however, Army initiatives in network science should be grounded in basic research as follows: Recommendation 1d. The initiatives recommended in 1, 1a, 1b, and 1c should include not only theoretical studies
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Network Science TABLE ES-1 Network Research Areas Research Area Key Objective Time Frame Commercial Interest Priority for Army Investment Modeling, simulating, testing, and prototyping very large networks Practical deployment tool sets Mid term High High Command and control of joint/combined networked forces Networked properties of connected heterogeneous systems Mid term Medium High Impact of network structure on organizational behavior Dynamics of networked organizational behavior Mid term Medium High Security and information assurance of networks Properties of networks that enhance survival Near term High High Relationship of network structure to scalability and reliability Characteristics of robust or dominant networks Mid term Medium Medium Managing network complexity Properties of networks that promote simplicity and connectivity Near term High High Improving shared situational awareness of networked elements Self-synchronization of networks Mid term Medium High Enhanced network-centric mission effectiveness Individual and organizational training designs Far term Medium Medium Advanced network-based sensor fusion Impact of control systems theory Mid term High Medium Hunter-prey relationships Algorithms and models for adversary behaviors Mid term Low High Swarming behavior Self-organizing UAV/UGV; self-healing Mid term Low Medium Metabolic and gene expression networks Soldier performance enhancement Near term Medium Medium but also the experimental testing of new ideas in settings sufficiently realistic to verify or disprove their use for intended applications. By selecting from Recommendations 1a through 1c an option that is ambitious yet achievable, the Army can lead the country in creating a base of knowledge about network science that is adequate to support applications on which both the Army and the country at large depend. The Army has another investment scenario that it could pursue: “building the base” for network science by funding a small program of basic research in network science. This investment of small amounts of Army risk capital funds would create a base of knowledge and personnel from which the Army could launch an attack on practical problems that arise as it tries to provide NCO capabilities. If the Army is limited to modest changes in the funding of its R&D portfolio and incremental changes to the way that it manages these investments, funding only a small program of basic research in network science could still have a significant effect. But the committee wants to be crystal clear that investments in basic (6.1) research in network science have no immediate prospects of impacting the design, test, evaluation, and sourcing of NCO capabilities. The main values created by a basic research investment would include access to thought leaders (principal investigators) in the university community, the training of students through their work on university projects, the development of a community that the Army can access to address its practical problems, and the efficient use of research dollars to impact multiple areas of application. To exploit these opportunities, the committee offers the following two recommendations: Recommendation 2. The Army should make a modest investment of at least $10 million per year to support a diverse portfolio of basic (6.1) network research that promises high leverage for the dollars invested and is clearly different from existing investments by other federal agencies like the National Science Foundation (NSF), the Department of Energy (DOE), and the National Institutes of Health (NIH). This modest level of investment is compatible with the Army’s current R&D portfolio. There is an adequate supply of promising research topics and talented researchers to make this investment productive. Additionally, it can be implemented within the Army’s current R&D management work processes. To identify the topics in basic network science research that would bring the most value to NCO, the committee recalls that the open system architectures for computer net-
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Network Science works consist of layers, each of which performs a special function regarded as a “service” by the layers above. It is useful to distinguish among the lower (physical and transport) layers of this architecture, the higher (applications) layers that are built on top of them to offer services to people, and the cognitive and social networks that are built higher still, on top of the services-to-humans layers. Research on the lower layers of the network architecture is relatively mature. Improving these levels is more of an engineering problem than one requiring basic research. The most immediate payoffs from network science are likely to result from research associated with the upper levels of the network architecture and the social networks that are built at an even higher level. This is where the committee thinks that Army investments are most likely to create the greatest value. An area of particular promise that has little or no current investment is the social implications of NCO for the organizational structure and command and control. Basic research could provide valuable insight into how military personnel use advanced information exchange capabilities to improve combat effectiveness. For example, one might study how troops in combat could use these capabilities to make better decisions. Additional basic research in the core content of network science might help to determine how the Army can most productively utilize the capabilities of its advanced information infrastructure. Recommendation 3. The Army should fund a basic research program to explore the interaction between information networks and the social networks that utilize them. The Army can implement Recommendations 2 and 3 within the confines of its present policies and procedures. They require neither substantial replanning nor the orchestration of joint Army/university/industry research projects. They create significant value and are actionable immediately. The committee’s Recommendations 1, 1a through 1d, 2, and 3 give the Army an actionable menu of options that span the opportunity space available. By selecting and implementing appropriate items from this menu, the Army can develop a robust network science to “enable progress toward achieving Network Centric Warfare capabilities,” as requested in the statement of task.
Representative terms from entire chapter: