<p>Peer-to-Peer (P2P) computing is a recent hot topic in the areas of networking and distributed systems. Work on P2P computing was triggered by a number of ad-hoc systems that made the concept popular. Later, academic research efforts started to investigate P2P computing issues based on scientific principles. Some of that research produced a number of structured P2P systems that were collectively referred to by the term ``Distributed Hash Tables'' (DHTs). However, the research occurred in a diversified way leading to the appearance of similar concepts yet lacking a common perspective and not heavily analyzed. In this thesis we present a number of papers representing our research results in the area of structured P2P systems grouped as two sets labeled respectively ``Designs'' and ``Analyses''.</p><p>The contribution of the first set of papers is as follows. First, we present the principle of distributed k-ary search (DKS) and argue that it serves as a framework for most of the recent P2P systems known as DHTs. That is, given the DKS framework, understanding existing DHT systems is done simply by seeing how they are instances of that framework. We argue that by perceiving systems as instances of the DKS framework, one can optimize some of them. We illustrate that by applying the framework to the Chord system, one of the most established DHT systems. Second, We show how the DKS framework helps in the design of P2P algorithms by two examples: (a) The DKS(n;k;f) system which is a system designed from the beginning on the principles of distributed k-ary search. (b) Two broadcast algorithms that take advantage of the distributed k-ary search tree.</p><p>The contribution of the second set of papers is as follows. We account for two approaches that we used to evaluate the performance of a particular class of DHTs, namely the one adopting periodic stabilization for topology maintenance. The first approach was of an intrinsic empirical nature. In that approach, we tried to perceive a DHT as a physical system and account for its properties in a size-independent manner. The second approach was of a more analytical nature. In this approach we applied the technique of Master equations, which is a widely used technique in the analysis of natural systems. The application of the technique lead to a highly accurate description of the behavior of structured overlays.</p><p>Additionally, the thesis contains a primer on structured P2P systems that tries to capture the main ideas that are prevailing in the field and enumerates a subset of the current hot and open research issues.</p>

Traffic simulation is an important tool for modelling the operations of dynamic traffic systems and helps analyse the causes and potential solutions of traffic problems such as congestion and traffic safety. Microscopic simulation models provide a detailed representation of the traffic process, which makes them most suitable for evaluation of complicated traffic facilities and Intelligent Transportation Systems that often consist of complex traffic management, safety and information systems. Macroscopic and mesoscopic models on the other hand, capture traffic dynamics in lesser detail, but are faster and easier to apply and calibrate than microscopic models. Therefore they are most suitable for modelling large networks, while microscopic models are usually applied to smaller areas. The objective of this thesis is to combine the strengths of both modelling approaches and diminish their individual weaknesses by constructing a hybrid mesoscopic-microscopic model that applies microscopic simulation to areas of specific interest, while simulating a surrounding network in lesser detail with a mesoscopic model. Earlier attempts at hybrid modelling have concentrated on integrating macroscopic and microscopic models and have proved difficult due to the large difference between the continuous-flow representation of traffic in macroscopic models and the detailed vehicle-and driver-behaviour represented in microscopic models. These problems are solved in this thesis by developing a mesoscopic vehicle-based and event-based model that avoids the (dis)aggregation problems of traffic flows at the inter-model boundaries. In addition, this thesis focuses on the general problems of consistency across the entire hybrid model. The requirements are identified that are important for a hybrid model to be consistent across the models at different levels of detail. These requirements vary from network and route-choice consistency to consistency of traffic dynamics across the boundaries of the micro- and mesoscopic submodels. An integration framework is proposed that satisfies these requirements. This integration framework has been implemented in a prototype hybrid model, MiMe, which is used to demonstrate the correctness of the solutions to the various integration issues. The hybrid model integrates MITSIMLab, a microscopic traffic simulation model, and Mezzo, the newly developed mesoscopic model. Both the hybrid model and the new Mezzo model are applied in a number of case studies, including a network in the North of Stockholm, which show their validity and applicability. The results are promising and support both the proposed integration architecture and the importance of integrating microscopic and mesoscopic models. / QC 20100520

As computing devices and wireless connectivity become ubiquitous, new usage scenarios emerge, where wireless communication links between mobile devices are established in an ad-hoc manner. The resulting wireless ad-hoc networks differ from classical computer networks in a number of ways, lack of permanent access to the global network and heterogeneous structure being some of them. Therefore, security services and mechanisms that have been designed for classical computer networks are not always the optimal solution in an ad-hoc network environment. The research is focused on analyzing how standard security services that are available in classical networks can be provided in an ad-hoc wireless network environment. The goal is to design a security system optimized for operation in ad-hoc wireless networks that provides the same security services – authentication, access control, data confidentiality and integrity, non-repudiation – currently available in classic wired networks. The first part of the thesis is the design and implementation of a security platform based on generic secure objects. The flexible and modular nature of this platform makes it suitable for deployment on devices that form ad-hoc networks – ranging from Java-enabled phones to PDAs and laptops. We then investigate the problems that appear when implementing in ad-hoc networks some of the security technologies that are standard building blocks of secure systems in classical computer networks. Two such technologies have been found to present problems, namely the areas of certification and access control. In a series of articles, we have described the problems that appear and devised solutions to them by designing protocols, techniques and extensions to standards that are optimized for usage in the ad-hoc network environment. These techniques, together with the functionality provided by the underlying security platform, are used to implement all standard security services – confidentiality, authentication, access control, non repudiation and integrity, allowing to integrate ad-hoc networks into the existing security infrastructure. / QC 20101001

<p>This thesis presents the design, implementation, and evaluation of Flow Java, a programming language for the implementation of concurrent programs. Flow Java adds powerful programming abstractions for automatic synchronization of concurrent programs to Java. The abstractions added are single assignment variables (logic variables) and futures (read-only views of logic variables).</p><p>The added abstractions conservatively extend Java with respect to types, parameter passing, and concurrency. Futures support secure concurrent abstractions and are essential for seamless integration of single assignment variables into Java. These abstractions allow for simple and concise implementation of high-level concurrent programming abstractions.</p><p>Flow Java is implemented as a moderate extension to the GNU GCJ/libjava Java compiler and runtime environment. The extension is not speci c to a particular implementation, it could easily be incorporated into other Java implementations.</p><p>The thesis presents three implementation strategies for single assignment variables. One strategy uses forwarding and dereferencing while the two others are variants of Taylor's scheme. Taylor's scheme represents logic variables as a circular list. The thesis presents a new adaptation of Taylor's scheme to a concurrent language using operating system threads.</p><p>The Flow Java system is evaluated using standard Java benchmarks. Evaluation shows that in most cases the overhead incurred by the extensions is between 10% and 50%. For some pathological cases the runtime increases by up to 150%. Concurrent programs making use of Flow Java's automatic synchronization, generally perform as good as corresponding Java programs. In some cases Flow Java programs outperform Java programs by as much as 33%.</p>

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This thesis presents the design, implementation, and evaluation of Flow Java, a programming language for the implementation of concurrent programs. Flow Java adds powerful programming abstractions for automatic synchronization of concurrent programs to Java. The abstractions added are single assignment variables (logic variables) and futures (read-only views of logic variables). The added abstractions conservatively extend Java with respect to types, parameter passing, and concurrency. Futures support secure concurrent abstractions and are essential for seamless integration of single assignment variables into Java. These abstractions allow for simple and concise implementation of high-level concurrent programming abstractions. Flow Java is implemented as a moderate extension to the GNU GCJ/libjava Java compiler and runtime environment. The extension is not speci c to a particular implementation, it could easily be incorporated into other Java implementations. The thesis presents three implementation strategies for single assignment variables. One strategy uses forwarding and dereferencing while the two others are variants of Taylor's scheme. Taylor's scheme represents logic variables as a circular list. The thesis presents a new adaptation of Taylor's scheme to a concurrent language using operating system threads. The Flow Java system is evaluated using standard Java benchmarks. Evaluation shows that in most cases the overhead incurred by the extensions is between 10% and 50%. For some pathological cases the runtime increases by up to 150%. Concurrent programs making use of Flow Java's automatic synchronization, generally perform as good as corresponding Java programs. In some cases Flow Java programs outperform Java programs by as much as 33%. / <p>QCR 20161026</p>

QC 20101201

Students today lack both time and money. At the same time e-commerce is increasing, and especially food sales over the internet. This report aims to explore the possibilities of a service that offers students a simple alternative for high quality food within their budget in the form of a web application. Students at Campus Valla expressed the need for such a service through a market research. The study was conducted by researching theories regarding usability and navigability. Students as a group often lack time and are used to getting fast and clear information; this is ensured by good navigability. After the researching of theories, several user tests were conducted on the targeted group. The result following this was the development of the web application Heat n' Eat. In order to achieve good navigability, the application was implemented with a simple layout, focusing on the products. A final user test showed that the application could be considered usable with focus on navigability. / Studenter idag har brist på både tid och pengar. Samtidigt ökar e-handeln och specifikt matförsäljningen över internet. Rapporten har som avsikt att undersöka möjligheterna för en tjänst, i form av en webbapplikation, som erbjuder studenter högkvalitativ mat inom deras budget på ett enkelt sätt. Via en marknadsundersökning på Campus Valla uttryckte studenter avsaknad av en sådan tjänst. Studien genomfördes genom att ta fram teori rörande användbarhet och navigerbarhet. Studenter som grupp har ofta ont om tid och är vana vid att få snabb och tydlig information vilket god navigerbarhet säkerställer. Efter teoristudien genomfördes användartester på målgruppen. Som ett resultat utvecklades webbapplikationen Heat n’ Eat. För att uppnå god navigerbarhet blev utformningen en simpel struktur med produkterna i fokus. Ett avslutande användartest visade att webbapplikationen kan anses vara användbar med fokus på navigerbarhet.

Very Small Enterprises (VSEs) are currently the backbone of all industries, since they account for roughly 80% of the world’s economy. In some countries, they account for over 95% of all companies and enterprises. As such, VSEs are a fundamental element in any given industry. Because of this, understanding how VSEs function and how, as a software developer, work and think is crucial to facilitate the software development process. A software unaware VSE (SUVSE) is a company which has little tangency with understanding software in general. The problem lies in how to properly and efficiently communicate with SUVSE, due to their limitations, as well as the general lack of knowledge regarding software development.   This report will cover the topic of challenges faced when working with a very small company for gathering domain knowledge (DK) and facilitating the communication and exchange of meaningful information, in the context of developing a software product, using agile methodologies. In the report, some of the more popular agile methodologies will be covered and chosen, in addition to existing ISO standards for VSEs.   The purpose of the research is to answer the following questions:   What topics are software unaware very small enterprise (SUVSE) aware of, in the software development process?   Which aspects of the software development process must be known by a software unaware domain expert of a very small enterprise (VSE), so that a software development team can capture the required domain knowledge (DK)?     How is the software unaware very small enterprises (SUVSEs) understanding of the software development process affected by their involvement in an agile development methodology?   To fulfill the purpose of the study, a case study was performed using 3 techniques to gather data: questionnaire, observation and interview. The participants were employees and CEOs from a few VSEs, contacted either via phone or face-to-face meetings.   The study showed the problems faced when working with SUVSE, what steps should be performed to facilitate communication with domain experts for gathering DK, and how the VSE can benefit from the knowledge and experience gained because of actively participating in the software development process. It concludes with practices on how to improve communication between software developers and VSE stakeholders to optimize the exchange of meaningful data and knowledge in the context of VSEs, and recommends future work based on the findings.

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