# Dynamic Data Driven Applications Systems

Dynamic Data Driven Applications Systems ("DDDAS") is a paradigm whereby the computation and instrumentation aspects of an application system are dynamically integrated with a feedback control loop, in the sense that instrumentation data can be dynamically incorporated into the executing model of the application (in targeted parts of the phase-space of the problem to either replace parts of the computation to speed-up the modeling or to make the model more accurate for aspects of the system not well represented by the model; this can be considered as the model "learning" from such dynamic data inputs), and in reverse the executing model can control the system's instrumentation to cognizantly and adaptively acquire additional data (or search through archival data), which in-turn can improve or speedup the model (modeling process). DDDAS-based approaches have been shown that they can enable more accurate and faster modeling and analysis of the characteristics and behaviors of a system and can exploit data in intelligent ways to convert them to new capabilities, including decision support systems with the accuracy of full-scale modeling, executing model-driven adaptive management of complex instrumentation (including adaptive coordination across multitudes of heterogeneous sensors and controllers), as well as efficient data collection, management, and data mining.
The power of the DDDAS paradigm is that it involves a dynamically adapting and system-cognizant model (for example a model cognizant of the physics of the system, or other inherent characteristics and representations of the system), which "learns" and adapts through the "dynamic data" inputs at execution time, can discern false data and avoids the pitfalls of traditional Machine Learning approaches which can go rogue. Moreover, unlike ML methods, DDDAS enables more accurate and faster modeling and analysis, for "systems analytics" rather than simply "data analytics", and the DDDAS computational and instrumentation frameworks, include in addition to comprehensive system-characteristics cognizant representations and models, software and hardware (computational and instrumentation) platforms architectures and services, and can also include the human-in-the-loop, as complex systems typically involve.
DDDAS-based approaches have demonstrated new capabilities in systems modeling and instrumentation, as well as autonomic capabilities in many areas, ranging from fundamental studies in materials properties (e.g., nanomaterials), to structural and civil engineering (e.g., smart buildings) and aerospace, to manufacturing (process planning and control; additive manufacturing), transportation systems, energy systems (e.g., smart power-grids), environmental (e.g., wildfires), weather (atmospheric and space), medical diagnosis and treatment, cloud computing, IoT, and communications systems, cybersecurity, and more. The DDDAS site contains links on the extensive work and impact of the DDDAS paradigm.

## History

The DDDAS concept - and the term - is claimed by Frederica Darema who initiated the efforts within the National Science Foundation (NSF), organizing a workshop in March 2000, with Profs Craig Douglas and Abhi Deshmukh as academic co-chairs. Around 2008, Darema introduced the term Infosymbiotics or Infosymbiotic Systems to denote DDDAS. Many researchers in academia, industry, and labs were influenced to adopt the DDDAS concept and the term under Dr. Darema's programs, starting from the mid-1990', at DARPA, NSF (including multi-agency programs), and AFOSR. Dr. Blasch continued the program after he became Program Manager at AFOSR upon Dr. Darema becoming the Director of AFOSR in 2016. Thus, the community advanced systems capabilities and concepts are under the rubric of DDDAS.
Starting in 2000, Dr. Darema led the community in organizing several DDDAS forums; these include a series of DDDAS Workshops, Symposia, Panels, and other related activities, for example, in conjunction with the International Conference in Computational Sciences (ICCS) with Profs. Craig Douglas and Abani Patra, the International Parallel and Distributed Computing Symposium (IPDPS), the Winter Simulation Conferences (WSC). Dennis Bernstein, Puneet Singla, and Sai Ravela led sessions at the American Controls Conference (ACC) 2014. Dr. Ravela organized a related Dynamic Data-driven Environmental Systems Science conference, DyDESS 2014 (MIT), and then proposed and ran DDDAS 2016 (Hartford), which included participation by United Technologies Research Center, followed by DDDAS 2017 (MIT) and 2020 (Online) conferences, and hosted the 2022 (MIT) conference, organizing a new collocated Earth, Planets, Climate, and Life theme, CLEPS22 (with more planned in the future). Since 2016, Dr. Blasch has organized numerous DDDAS and other associated forums (e.g., Fusion2015 and follow-up Conference series). The 2024 conference DDDAS2024 is run by Prof. Dimitris Metaxas at Rutgers University (with more planned in the future), with conference proceedings published by Springer. Other work is presented in the DDDAS Handbook series by Springer. A more complete list of DDDAS forums and other activities is provided in the DDDAS site.

## Related concepts

The DDDAS concept's proposers have rarely related the "feedback control between an executing model of a system with its instrumentation" framing to other approaches. For example, it has been pointed out that it relates to "intelligent data assimilation, steered data assimilation, solution-based engineering science (SBES), cyber-physical sciences (CPS), etc." (see here). However, DDDAS does strongly relate to several prior and contemporary concepts:
* DDDAS is a derivative of seminal ideas presented in the late 1950s to 1970s, such as by Chertoff on Sequential Design of Experiments, and by Fedorov on Design of Experiments (1970s), where the experiments determine the parameters and the parameters guide the experiments, including for data and model selection - these approaches sequentially adjust the models in response to observations and dynamically design experiments in a closed loop to incorporate new observations, see Theory of Optimal Experiments
* Learning methods (starting in the 1980s and 1990s). DDDAS relates to the concept of active learning, which "formally studies the closed-loop phenomenon of a learner selecting actions or making queries that influence what data" trains the model. Active sampling strategies based on information gain are common in active and adaptive learning and relate to the design of experiments, e.g., Cohn's work (1994).
* DDDAS relates to Reinforcement Learning (starting in the mid-1990s) in model-based settings, where the model of the system is learned in addition to actively optimizing environmental exploration strategies (for example, the Dyna algorithm). Nevertheless, there is less emphasis on the "control of the system instrumentation" as in DDDAS.
* DDDAS relates to data assimilation (a branch of Estimation Theory) coupled with Adaptive Observations (the 1990s), where observation data and their uncertainty are used to estimate model states and parameters (globally, at multiple scales, or locally) in the phase space. The reverse aspect in the DDDAS feedback control loop—the model adaptively controlling the instrumentation—is naturally associated with Targeting Observations. For example, the Data Assimilation and Adaptive Observation, MIT Thesis 1999 discusses assimilating supplementary targeted observations dynamically using forecasts and their uncertainties.
* MacKay's Information-based Active Data Selection (1991) employs Bayesian methods to determine expected informativeness of candidate measurements is used to select salient ones for learning, improving the expected informativeness. And, Information Retrieval (in the 90s), where queries generate searches, and the results refine the queries with relevance feedback.