A Taxonomy of Data Grids for Distributed Data Sharing, Management and Processing

Data Grids have been adopted as the platform for scientific communities that need to share, access, transport, process and manage large data collections distributed worldwide. They combine high-end computing technologies with high-performance networking and wide-area storage management techniques. In this paper, we discuss the key concepts behind Data Grids and compare them with other data sharing and distribution paradigms such as content delivery networks, peer-to-peer networks and distributed databases. We then provide comprehensive taxonomies that cover various aspects of architecture, data transportation, data replication and resource allocation and scheduling. Finally, we map the proposed taxonomy to various Data Grid systems not only to validate the taxonomy but also to identify areas for future exploration. Through this taxonomy, we aim to categorise existing systems to better understand their goals and their methodology. This would help evaluate their applicability for solving similar problems. This taxonomy also provides a "gap analysis" of this area through which researchers can potentially identify new issues for investigation. Finally, we hope that the proposed taxonomy and mapping also helps to provide an easy way for new practitioners to understand this complex area of research.Comment: 46 pages, 16 figures, Technical Repor

Cache Serializability: Reducing Inconsistency in Edge Transactions

Read-only caches are widely used in cloud infrastructures to reduce access latency and load on backend databases. Operators view coherent caches as impractical at genuinely large scale and many client-facing caches are updated in an asynchronous manner with best-effort pipelines. Existing solutions that support cache consistency are inapplicable to this scenario since they require a round trip to the database on every cache transaction. Existing incoherent cache technologies are oblivious to transactional data access, even if the backend database supports transactions. We propose T-Cache, a novel caching policy for read-only transactions in which inconsistency is tolerable (won't cause safety violations) but undesirable (has a cost). T-Cache improves cache consistency despite asynchronous and unreliable communication between the cache and the database. We define cache-serializability, a variant of serializability that is suitable for incoherent caches, and prove that with unbounded resources T-Cache implements this new specification. With limited resources, T-Cache allows the system manager to choose a trade-off between performance and consistency. Our evaluation shows that T-Cache detects many inconsistencies with only nominal overhead. We use synthetic workloads to demonstrate the efficacy of T-Cache when data accesses are clustered and its adaptive reaction to workload changes. With workloads based on the real-world topologies, T-Cache detects 43-70% of the inconsistencies and increases the rate of consistent transactions by 33-58%.Comment: Ittay Eyal, Ken Birman, Robbert van Renesse, "Cache Serializability: Reducing Inconsistency in Edge Transactions," Distributed Computing Systems (ICDCS), IEEE 35th International Conference on, June~29 2015--July~2 201

A Human-Centric Approach to Group-Based Context-Awareness

The emerging need for qualitative approaches in context-aware information processing calls for proper modeling of context information and efficient handling of its inherent uncertainty resulted from human interpretation and usage. Many of the current approaches to context-awareness either lack a solid theoretical basis for modeling or ignore important requirements such as modularity, high-order uncertainty management and group-based context-awareness. Therefore, their real-world application and extendability remains limited. In this paper, we present f-Context as a service-based context-awareness framework, based on language-action perspective (LAP) theory for modeling. Then we identify some of the complex, informational parts of context which contain high-order uncertainties due to differences between members of the group in defining them. An agent-based perceptual computer architecture is proposed for implementing f-Context that uses computing with words (CWW) for handling uncertainty. The feasibility of f-Context is analyzed using a realistic scenario involving a group of mobile users. We believe that the proposed approach can open the door to future research on context-awareness by offering a theoretical foundation based on human communication, and a service-based layered architecture which exploits CWW for context-aware, group-based and platform-independent access to information systems

Mechanisms of Security: Locks, keys, and ordered life in Iron Age Norway (c. 0–1050 AD)

This thesis examines the technological and social parameters for, and the social impact of, the introduction and implementation of locking into Norway in the Iron Age, based on analyses of locks and keys. The functional properties of locking devices and their practical applications as security mechanisms constitute the focal point of the study, and the basis for discussing how locking contributed to the ordering and organisation of life and society in the course of the first millennium AD. The main aims are to establish an empirical foundation for the study of locking devices and to understand locks and keys as a technological and social phenomenon which was affected by and had effects on the societies that created and used them. The archaeological material is approached from a conceptual framework centred on perspectives of entanglement and social boundaries, in which locking is considered a social practice. As material agents locks and keys are seen as involved in the physical protection of things and spaces, regulation of access, and manifestation of ownership rights, as well as the creation and negotiation of values and norms as part of social order. The analytical material is comprised by more than eight hundred locks and keys dated from the Roman Period to the Viking Age, deriving from burials, depositions, and settlements, as well as single finds. The finds are used in the construction of renewed classifications for Scandinavian locks and keys, which is based on their functional designs and their correlation to lockable containers, doors, and fetters. Through temporal, spatial, and contextual analyses of types the thesis outlines a complex picture of production, innovation, distribution, and application of locking devices. The results illustrate that locks and keys were introduced and developed in stages in Norway, and that their use expanded and diversified practically as well as socially. The analytical patterns are further discussed in terms of security, ownership, and order, arguing that locking from its introduction became gradually embedded into society during the Iron Age. This is suggested to result from the success of locks and keys in achieving order, and their close relationship with processes of hierarchisation, social differentiation, and social complexity. The thesis provides new insights into the practical functions and applications of diverse locking mechanisms, technological development, craft specialisation, exchange and contact networks, and the social impact of locking in terms of physical and social order. It also contributes to current debates concerning social organisation and transformations within Norway and wider Scandinavia and Northern Europe in the first millennium AD.Doktorgradsavhandlin

Evaluating Job Search Programs for Old and Young Individuals: Heterogeneous Impact on Unemployment Duration

This paper exploits an area-based pilot experiment to identify average treatment effects on unemployment duration of treated individuals of two active labor market programs implemented in Portugal. We focus on the short-term heterogeneous impact on two subpopulations of unemployed individuals: young (targeted by the Inserjovem program) and old (targeted by the Reage program). We show that the latter program has a small and positive impact (reduction) on unemployment duration of workers finding a job upon participation, whereas the impact of Inserjovem is generally negative (extended durations). These results are robust to a wide variety of constructions of quasi-experimental settings and estimators. The identification of heterogeneous effects showed that the program results were less satisfactory for young workers, for those over 40 and for the less educated. Women also benefited less from the programs. The results seem to improve slightly for young workers in the 2nd semester of implementation, but they deteriorate in the medium term. The lack of wage subsidies in the Portuguese programs may explain the minor impacts obtained, when compared to similar programs

Developing Android Mobile Map Application with standard navigation tools for pedestrians

Advanced features of modern mobile devices have made it possible to develop and use maps and map based applications for navigation purposes. Since most mobile map applications nowadays are developed for motor vehicles, there is a demand for portable pedestrian navigation applications. In this thesis the Android mobile map application with standard navigation tools for pedestrian navigation was developed, as a platform for facilitating the Lund Challenge location based demonstrator of the HaptiMap project. The pivotal aim of the Lund Challenge demonstrator is to make the sights of Lund city more accessible. The mobile phone application is being designed as a touristic, historical location based game which will also assist tourists to navigate themselves in the city. To enable exploration of historical and current sites of Lund the demonstrator should contain basic components of exploring and way finding. Prior to the development the OpenStreetMap (OSM) road network data and Swedish National Road Database (NVDB) were introduced. The main advantage of using the OSM data over the NVDB dataset is the completeness of the OSM data in terms of pedestrian paths. The datasets were imported to PostgreSQL spatially extended PostGIS database, where different routing algorithms provided by pgRouting were used for routing calculations. As the Lund Challenge demonstrator is intended not only for general users but also for visually impaired users, the problem of user navigation in the parks and open areas were also discussed and the feasibility study was performed. The limitation of the developed application was the problem of the user navigation in the parks and open areas. It is therefore necessary to upgrade the road database with possible path in the open areas and parks in order to implement this application.Advanced features of modern devices have made it possible to develop and use maps and map-based applications for navigation purposes. Since most mobile map applications are currently developed for motor vehicles, there is a demand for portable pedestrian navigation applications. In this thesis, a mobile map application was developed with standard navigation tools for pedestrians, which can be used with mobile phones running Android Operating System. The application will be used as a platform for facilitating the Lund Challenge location based demonstrator. Lund Challenge location based demonstrator is designed to make historical and actual maps of Lund more accessible and is a part of the HaptiMap project. This project aims to create maps and develop location-based services for all users, including elderly and visually impaired. The goal of the Lund Challenge location based demonstrator (also known as The Lund Time Machine) is to minimize the efforts of pedestrians, especially tourists, with finding interesting sites around the city. Initially, it is being designed as a historical location based game which will assist tourists to navigate themselves around the city. In order to further explore historical and current sites, the Lund Challenge should be enhanced with the basic features of exploration and navigation included in this thesis. The road network data was chosen from two available sources: 1) data from OpenStreetMap (OSM) project which provides free geographic data, and 2) The Swedish National Road Database (NVDB) authorized by the Swedish government, which includes all Swedish road network and selected cycle paths. For this thesis, analysis was performed on the datasets using different shortest path algorithms for routing calculations. A primary advantage of using OSM over NVDB is the completeness of data relating to pedestrian paths. As a result, the determination was made that the OSM option was more appropriate for the purpose of this thesis. Since the Lund Challenge location based demonstrator is intended for both general and visually impaired users, the problem of user navigation in parks and open areas was also discussed and a feasibility study was performed. This study revealed a limitation in the application with user navigation in parks and open areas. To resolve this, it is necessary to upgrade the road network with all possible pedestrian paths for parks and open areas