Empirically characterizing evolvability and changeability in engineering systems

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012."June 2012." Cataloged from PDF version of thesis.Includes bibliographical references (p. 205-212).The beginning phases of system development and conceptual design require careful consideration, as these decisions will have significant influence on system lifetime performance and are often made with incomplete system knowledge. Decision makers may improve their capacity to discriminate between system concepts and design choices by measuring a system's "ilities" such as changeability, evolvability, and survivability. These ilities may enable systems to respond to perturbations in the design space, context space, and needs space in order to ensure system functionality and adequate performance over time. A system may be designed to change in response to perturbations, or remain statically robust/survivable to perturbations in order to avoid deficiencies or failures. This research attempts to analyze the mechanisms that allow system changes to occur. More specifically, this research will further the characterization of system changeability and evolvability and ultimately provide a structured and meaningful way of classifying system characteristics often described as "ilities". Value sustainment is proposed as an ultimate goal of systems, providing value in spite of perturbations in design, context, or needs. The premise of value sustainment is investigated through four distinct research thrusts: 1) a basis for defining system changes and ilities; 2) a system change examples database with categorical cluster analysis case research; 3) epoch-shift, impact, response, outcome case research; and 4) expert interviews case research. Focusing on change-related ilities, this research proposes constructs for identifying and enabling vague, yet desirable, system properties. Evolvability is characterized as a subset of changeability and defined as the ability of an architecture to be inherited and changed across generations [over time], with a set of ten proposed design principles including decentralization, redundancy, targeted modularity, scalability, integrability, reconfigurability, mimicry, leverage ancestry, disruptive architectural overhaul, and resourceful exaptation.by Jay Clark Beesemyer, Jr.S.M

An Empirical Investigation of System Changes to Frame Links between Design Decisions and Ilities

Maintaining system performance in the presence of uncertainties in design and operating environments is both challenging and increasingly essential as system lifetimes grow longer. In response to perturbations brought on by these uncertainties, such as disturbances, context shifts, and shifting stakeholder needs, systems can continue to deliver value by being either robust or changeable. These lifecycle properties, sometimes called “ilities”, have been proposed as means to achieve system value sustainment in spite of changes in contexts or needs. Intentionally designing for these lifecycle properties is an active area of research, and no consensus has formed regarding how these and other “ilities” might trade off. This paper describes ongoing research that investigates empirical examples of system changes in order to characterize these changes and to develop a categorization scheme for framing and clarifying design approaches for proactively creating ilities in a system. Example categories from the data for system changes include: the perturbation trigger for the change, the type of agent executing the system change, and the valid lifecycle phase for execution. In providing a structured means to identify system change characteristics, this paper informs future research by framing possible relationships between ilities and design choices that enable them.Massachusetts Institute of Technology. Systems Engineering Advancement Research Initiativ

Reading Maud’s remains: Tennyson, geological processes, and palaeontological reconstructions

As Tennyson's “little Hamlet ,” Maud (1855) posits a speaker who, like Hamlet, confronts the ignominious fate of dead remains. Maud's speaker contemplates such remains as bone, hair, shell, and he experiences his world as one composed of hard inorganic matter, such things as rocks, gems, flint, stone, coal, and gold. While Maud's imagery of “stones, and hard substances” has been read as signifying the speaker's desire “unnaturally to harden himself into insensibility” (Killham 231, 235), I argue that these substances benefit from being read in the context of Tennyson's wider understanding of geological processes. Along with highlighting these materials, the text's imagery focuses on processes of fossilisation, while Maud's characters appear to be in the grip of an insidious petrification. Despite the preoccupation with geological materials and processes, the poem has received little critical attention in these terms. Dennis R. Dean, for example, whose Tennyson and Geology (1985) is still the most rigorous study of the sources of Tennyson's knowledge of geology, does not detect a geological register in the poem, arguing that by the time Tennyson began to write Maud, he was “relatively at ease with the geological world” (Dean 21). I argue, however, that Maud reveals that Tennyson was anything but “at ease” with geology. While In Memoriam (1851) wrestles with religious doubt that is both initiated, and, to some extent, alleviated by geological theories, it finally affirms the transcendence of spirit over matter. Maud, conversely, gravitates towards the ground, concerning itself with the corporal remains of life and with the agents of change that operate on all matter. Influenced by his reading of geology, and particularly Charles Lyell's provocative writings on the embedding and fossilisation of organic material in strata in his Principles of Geology (1830–33) volume 2, Tennyson's poem probes the taphonomic processes that result in the incorporation of dead remains and even living flesh into the geological system