Doctor of Philosophy

dissertationWe propose a collective approach for harnessing the idle resources (cpu, storage, and bandwidth) of nodes (e.g., home desktops) distributed across the Internet. Instead of a purely peer-to-peer (P2P) approach, we organize participating nodes to act collectively using collective managers (CMs). Participating nodes provide idle resources to CMs, which unify these resources to run meaningful distributed services for external clients. We do not assume altruistic users or employ a barter-based incentive model; instead, participating nodes provide resources to CMs for long durations and are compensated in proportion to their contribution. In this dissertation we discuss the challenges faced by collective systems, present a design that addresses these challenges, and study the effect of selfish nodes. We believe that the collective service model is a useful alternative to the dominant pure P2P and centralized work queue models. It provides more effective utilization of idle resources, has a more meaningful economic model, and is better suited for building legal and commercial distributed services. We demonstrate the value of our work by building two distributed services using the collective approach. These services are a collective content distribution service and a collective data backup service

Sharing Economy Business Models : Addressing the design-implementation gap

Despite sharing being a long-practiced form of consumption, the concept ‘sharing economy’ has emerged only recently. New business models have proliferated, utilising technology to reduce transaction costs and facilitate shared access. Societal actors have taken interest in the sharing economy, to reduce resource consumption, foster social cohesion, and support the economy. However, sharing economy business models facilitate a wide array of consumption practices, including sharing, renting, borrowing, lending, bartering, swapping, trading, exchanging, gifting, buying second-hand, and even buying new goods. Past academic research and media attention tend to focus on unicorns such as Airbnb and Uber. There is greater need to explore the diverse permutations of business models within the sharing economy, especially considering sustainability.However, a gap exists between the design and successful implementation of sharing economy business models. This research aims to advance and structure knowledge about the sharing economy and sustainable business models, by using business modelling methods to study the design and implementation of sharing economy business models. Inspired by design science, this research engages in prescriptive theory-building and design- oriented research to construct and evaluate design artefacts. Incorporating data materials from people, documents, and literature, the research strategies of grounded theory and desk research are utilised to support methods for data collection and data analysis.The research proposes a prescriptive definition of the sharing economy as a socio-economic system that leverages technology to mediate two-sided markets, which facilitate temporary access to goods that are under- utilised, tangible, and rivalrous. From this, four design principles guide the formation of the sharing economy business model framework, which capture three value dimensions, sixteen business model attributes, and eighty- nine configuration options. This research proposes a coherent design theory to support the conceptualisation of sharing economy business models for sustainability.Additional artefacts are developed to support the successful implementation of these business models. First, business model patterns provide the justificatory knowledge to select relevant business model attributes in specific contexts. Then, a systematic framework measures the social impact of sharing platforms across four aspects – trust, empowerment, social justice, and inclusivity. Finally, organisational response strategies to COVID-19 are established in the sharing economy.The primary contribution of this research is conceptual, with additional modest methodological and empirical contributions. Furthermore, the artefacts are intended to be useful for research and practice, including scholars, entrepreneurs, managers, policymakers, investors, users, and concerned citizens

A HOLISTIC REDUNDANCY- AND INCENTIVE-BASED FRAMEWORK TO IMPROVE CONTENT AVAILABILITY IN PEER-TO-PEER NETWORKS

Peer-to-Peer (P2P) technology has emerged as an important alternative to the traditional client-server communication paradigm to build large-scale distributed systems. P2P enables the creation, dissemination and access to information at low cost and without the need of dedicated coordinating entities. However, existing P2P systems fail to provide high-levels of content availability, which limit their applicability and adoption. This dissertation takes a holistic approach to device mechanisms to improve content availability in large-scale P2P systems. Content availability in P2P can be impacted by hardware failures and churn. Hardware failures, in the form of disk or node failures, render information inaccessible. Churn, an inherent property of P2P, is the collective effect of the users’ uncoordinated behavior, which occurs when a large percentage of nodes join and leave frequently. Such a behavior reduces content availability significantly. Mitigating the combined effect of hardware failures and churn on content availability in P2P requires new and innovative solutions that go beyond those applied in existing distributed systems. To addresses this challenge, the thesis proposes two complementary, low cost mechanisms, whereby nodes self-organize to overcome failures and improve content availability. The first mechanism is a low complexity and highly flexible hybrid redundancy scheme, referred to as Proactive Repair (PR). The second mechanism is an incentive-based scheme that promotes cooperation and enforces fair exchange of resources among peers. These mechanisms provide the basis for the development of distributed self-organizing algorithms to automate PR and, through incentives, maximize their effectiveness in realistic P2P environments. Our proposed solution is evaluated using a combination of analytical and experimental methods. The analytical models are developed to determine the availability and repair cost properties of PR. The results indicate that PR’s repair cost outperforms other redundancy schemes. The experimental analysis was carried out using simulation and the development of a testbed. The simulation results confirm that PR improves content availability in P2P. The proposed mechanisms are implemented and tested using a DHT-based P2P application environment. The experimental results indicate that the incentive-based mechanism can promote fair exchange of resources and limits the impact of uncooperative behaviors such as “free-riding”

Multi-Agent Systems

This Special Issue ""Multi-Agent Systems"" gathers original research articles reporting results on the steadily growing area of agent-oriented computing and multi-agent systems technologies. After more than 20 years of academic research on multi-agent systems (MASs), in fact, agent-oriented models and technologies have been promoted as the most suitable candidates for the design and development of distributed and intelligent applications in complex and dynamic environments. With respect to both their quality and range, the papers in this Special Issue already represent a meaningful sample of the most recent advancements in the field of agent-oriented models and technologies. In particular, the 17 contributions cover agent-based modeling and simulation, situated multi-agent systems, socio-technical multi-agent systems, and semantic technologies applied to multi-agent systems. In fact, it is surprising to witness how such a limited portion of MAS research already highlights the most relevant usage of agent-based models and technologies, as well as their most appreciated characteristics. We are thus confident that the readers of Applied Sciences will be able to appreciate the growing role that MASs will play in the design and development of the next generation of complex intelligent systems. This Special Issue has been converted into a yearly series, for which a new call for papers is already available at the Applied Sciences journal’s website: https://www.mdpi.com/journal/applsci/special_issues/Multi-Agent_Systems_2019

Development of evidence-based behavioural interventions to reduce inappropriate use of antibiotics beyond clinical settings

Human use of antibiotics in China accounts for a quarter of worldwide antibiotic consumption and mainly occurs in outpatient and community settings. Non-clinical factors for antibiotic use are main drivers of its excessive consumption. To date, almost every intervention has focused exclusively on antibiotic prescribing behaviours, with little attention being paid to antibiotic consumer’s usage behaviours in the community. This PhD study aimed to develop an evidence-based, theory-informed behavioural change intervention to reduce inappropriate use of antibiotics in the Chinese communities. To conduct this programme of research, I employed a mixed-methods approach throughout the study phases, which included: 1) systematic literature reviews on determinants of antibiotic use in China and on behavioural change interventions to reduce unnecessary or inappropriate use of medical interventions, 2) secondary data analyses of large-scale population data on antibiotic use-related knowledge and practice, 3) formative interviews to ensure acceptability and feasibility of proposed interventions, and finally 4) a mixed-methods feasibility evaluation of the pilot intervention. The systematic reviews identified non-clinical factors and potential pathways influencing public’s antibiotic use, and the components of promising behavioural change interventions. Using the survey data, some of the pathways were quantitatively assessed to inform the development of a context-appropriate intervention - reducing access to non-prescription antibiotics in rural China was identified to be a priority. Additionally, (mis-)perceived antibiotic efficacy for upper respiratory tract infections (URTIs) was found to be associated with increased odds of antibiotic use in the community. The new knowledge contributed to the design of the proposed intervention. Working with local partners, I developed and conducted a feasibility assessment of a pilot antibiotic take-back programme aiming to reduce household antibiotic storage and unsafe disposal in rural China. The proposed intervention was deemed feasible and appropriate

Proceedings of RSEEM 2006 : 13th Research Symposium on Emerging Electronic Markets

Electronic markets have been a prominent topic of research for the past decade. Moreover, we have seen the rise but also the disappearance of many electronic marketplaces in practice. Today, electronic markets are a firm component of inter-organisational exchanges and can be observed in many branches. The Research Symposium on Emerging Electronic Markets is an annual conference bringing together researchers working on various topics concerning electronic markets in research and practice. The focus theme of the13th Research Symposium on Emerging Electronic Markets (RSEEM 2006) was ?Evolution in Electronic Markets?. Looking back at more than 10 years of research activities in electronic markets, the evolution can be well observed. While electronic commerce activities were based largely on catalogue-based shopping, there are now many examples that go beyond pure catalogues. For example, dynamic and flexible electronic transactions such as electronic negotiations and electronic auctions are enabled. Negotiations and auctions are the basis for inter-organisational trade exchanges about services as well as products. Mass customisation opens up new opportunities for electronic markets. Multichannel electronic commerce represents today?s various requirements posed on information and communication technology as well as on organisational structures. In recent years, service-oriented architectures of electronic markets have enabled ICT infrastructures for supporting flexible e-commerce and e-market solutions. RSEEM 2006 was held at the University of Hohenheim, Stuttgart, Germany in September 2006. The proceedings show a variety of approaches and include the selected 8 research papers. The contributions cover the focus theme through conceptual models and systems design, application scenarios as well as evaluation research approaches

Methods for improving resilience in communication networks and P2P overlays

Resilience to failures and deliberate attacks is becoming an essential requirement in most communication networks today. This also applies to P2P Overlays which on the one hand are created on top of communication infrastructures, and therefore are equally affected by failures of the underlying infrastructure, but which on the other hand introduce new possibilities like the creation of arbitrary links within the overlay. In this article, we present a survey of strategies to improve resilience in communication networks as well as in P2P overlay networks. Furthermore, our intention is to point out differences and similarities in the resilience-enhancing measures for both types of networks. By revising some basic concepts from graph theory, we show that many concepts for communication networks are based on well-known graph-theoretical problems. Especially, some methods for the construction of protection paths in advance of a failure are based on very hard problems, indeed many of them are in NP and can only be solved heuristically or on certain topologies. P2P overlay networks evidently benefit from resilience-enhancing strategies in the underlying communication infrastructure, but beyond that, their specific properties pose the need for more sophisticated mechanisms. The dynamic nature of peers requires to take some precautions, like estimating the reliability of peers, redundantly storing information, and provisioning a reliable routing