119,342 research outputs found

    Change escalation processes and complex adaptive systems: from incremental reconfigurations to discontinuous restructuring

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    This study examines when “incremental” change is likely to trigger “discontinuous” change, using the lens of complex adaptive systems theory. Going beyond the simulations and case studies through which complex adaptive systems have been approached so far, we study the relationship between incremental organizational reconfigurations and discontinuous organizational restructurings using a large-scale database of U.S. Fortune 50 industrial corporations. We develop two types of escalation process in organizations: accumulation and perturbation. Under ordinary conditions, it is perturbation rather than the accumulation that is more likely to trigger subsequent discontinuous change. Consistent with complex adaptive systems theory, organizations are more sensitive to both accumulation and perturbation in conditions of heightened disequilibrium. Contrary to expectations, highly interconnected organizations are not more liable to discontinuous change. We conclude with implications for further research, especially the need to attend to the potential role of managerial design and coping when transferring complex adaptive systems theory from natural systems to organizational systems

    Adaptive indexing in modern database kernels

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    Physical design represents one of the hardest problems for database management systems. Without proper tuning, systems cannot achieve good performance. Offline indexing creates indexes a priori assuming good workload knowledge and idle time. More recently, online indexing monitors the workload trends and creates or drops indexes online. Adaptive indexing takes another step towards completely automating the tuning process of a database system, by enabling incremental and partial online indexing. The main idea is that physical design changes continuously, adaptively, partially, incrementally and on demand while processing queries as part of the execution operators. As such it brings a plethora of opportunities for rethinking and improving every single corner of database system design. We will analyze the indexing space between offline, online and adaptive indexing through several state of the art indexing techniques, e. g., what-if analysis and soft indexes. We will discuss in detail adaptive indexing techniques such as database cracking, adaptive merging, sideways cracking and various hybrids that try to balance the online tuning overhead with the convergence speed to optimal performance. In addition, we will discuss how various aspects of modern techniques for database architectures, such as vectorization, bulk processing, column-store execution and storage affect adaptive indexing. Finally, we will discuss several open research topics towards fully automomous database kernels

    A Conceptual Architecture for Enabling Future Self-Adaptive Service Systems

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    Dynamic integration methods for unknown data sources and services at system design time are currently primarily driven by technological standards. Hence, little emphasis is being placed on integration methods. However, the combination of heterogeneous data sources and services offered by devices across domains is hard to standardize. In this paper, we will shed light on the interplay of self-adaptive system architectures as well as bottom-up, incremental integration methods relying on formal knowledge bases. An incremental integration method has direct influences on both the system architecture itself and the way these systems are engineered and operated during design and runtime. Our findings are evaluated in the context of a case study that uses an adapted bus architecture including two tool prototypes. In addition, we illustrate conceptually how control loops such as MAPE-K can be enriched with machine-readable integration knowledge

    Adaptive development and maintenance of user-centric software systems

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    A software system cannot be developed without considering the various facets of its environment. Stakeholders – including the users that play a central role – have their needs, expectations, and perceptions of a system. Organisational and technical aspects of the environment are constantly changing. The ability to adapt a software system and its requirements to its environment throughout its full lifecycle is of paramount importance in a constantly changing environment. The continuous involvement of users is as important as the constant evaluation of the system and the observation of evolving environments. We present a methodology for adaptive software systems development and maintenance. We draw upon a diverse range of accepted methods including participatory design, software architecture, and evolutionary design. Our focus is on user-centred software systems

    Determination of Behavior of Coupled Shear Walls Subjected to Horizontal Forces through Nonlinear Static Methods

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    Coupled shear walls are one of the systems commonly used in medium and highrise structures to resist lateral forces. Yet these systems should not collapse or be induced severe damage during earthquake actions. For this reason, coupled shear walls must have high strength, high ductility, high energy absorption capacity and high shear stiffness to limit lateral deformations. The recent advances in structural engineering have increased the interest in performance based design. In the study herein, hence, the performance based design of a coupled shear wall system has been carried out. The design has later been checked against nonlinear time history analysis and the design performed has been confirmed to be quite safe. In the second stage of the study, the horizontal capacity of couple shear walls is predicted by the pushover analyses. Though these procedures have been used for different types of structures, they have not been employed for coupled shear walls. The procedures employed are conventional pushover (deformation and forced based), force based adaptive pushover, and deformation based adaptive pushover. The capacity curves obtained through these procedures have been compared with the one determined through Incremental Dynamic Analysis. The evaluation shows that it is almost unlikely to determine the capacity curve of coupled shear walls by the nonlinear static analyses. Nonetheless, the displacement based adaptive pushover analyses has been able to predict the base shear capacity and capture the displacement profile of the system up to a certain level in the nonlinear region

    Robust observer design under measurement noise

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    We prove new results on robust observer design for systems with noisy measurement and bounded trajectories. A state observer is designed by dominating the incrementally homogeneous nonlinearities of the observation error system with its linear approximation, while gain adaptation and incremental observability guarantee an asymptotic upper bound for the estimation error depending on the limsup of the norm of the measuremen noise. The gain adaptation is implemented as the output of a stable filter using the squared norm of the measured output estimation error and the mismatch between each estimate and its saturated value
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