No abstract

Despite its ubiquity in the systems engineering literature, flexibility remains an ambiguous concept. There exist a multitude of definitions, which vary not only by domain, but within domains as well. Furthermore, these definitions often conflict with one another, making it difficult to discern the intended meaning in a given study or to form generalizations across studies. Complicating matters, there is a plethora of related terminology that is often used carelessly and/or interchangeably with flexibility. In this paper, we employ a novel ontological framework for clarifying salient aspects of extant flexibility-related terminology. While it was not possible to distill consensus definitions from the literature, we did identify certain dominant characteristics that enabled us to formulate a set of democratic definitions for flexibility, adaptability, and robustness, as well as recommended definitions for agility and versatility. We believe that the proposed definitions of these key system design principles may provide a baseline for improving analysis and communication among systems engineering practitioners and academics.

In recent years, attack trees have been developed to describe processes by which malicious users attempt to exploit or break computer software and/or networks. Attack trees are a way of decomposing, visualizing, and determining the cost or likeliness of attacks. Similarly, Petri Nets (PNs) are graphical representations of a system or process used for modeling, formal analysis, and design verification. PNs are easy to build and simulate using a myriad of available tools. There are a number of subclasses of PNs, including Colored, Timed, Stochastic, etc. This paper focuses on the use of Generalized Stochastic PNs (GSPNs) to model and analyze Attack Trees with the ultimate goal of automating the analysis using simulation tools.The results of this simulation and analysis can be used to further refine the Attack Tree or to develop countermeasures.

Quantum key distribution (QKD) is an innovative technology that exploits the laws of quantum mechanics to generate and distribute unconditionally secure shared key for use in cryptographic applications. However, QKD is a relatively nascent technology where real-world system implementations differ significantly from their ideal theoretical representations. In this paper, we introduce a modeling framework built upon the OMNeT++ discrete event simulation framework to study the impact of implementation nonidealities on QKD system performance and security. Specifically, we demonstrate the capability to study the device imperfections and practical engineering limitations through the modeling and simulation of a polarization-based, prepare and measure BB84 QKD reference architecture. The reference architecture allows users to model and study complex interactions between physical phenomenon and system-level behaviors representative of real-world design and implementation tradeoffs. Our results demonstrate the flexibility of the framework to simulate and evaluate current, future, and notional QKD protocols and components.

Predictive mental workload modeling is one established tool within the broad systems engineering activity of Human Systems Integration (HSI). Using system architecture as the foundation, this paper explores the use of Multiple Resource Theory to create representative workload models for evaluating operational system‐of‐systems (SoS) concepts. Through careful consideration of task demands, conflict generated between tasks, and workload mitigation strategies, informed design decision can improve overall human‐system performance. An example involving a single pilot controlling multiple remotely piloted aircraft (RPA) is presented to illustrate the use of workload modeling. Several observations are made that drive measurably excessive workload: multitasking, communications, continuously updating situational awareness and mission planning. In addition, three metrics are proposed for incorporating human workload analysis during system design. This technique has applicability across a wide range systems‐of‐systems and operational concepts involving complex human‐system interactions. © 2012 Wiley Periodicals, Inc. Syst Eng 15