Peer Data Management

Peer Data Management (PDM) deals with the management of structured data in unstructured peer-to-peer (P2P) networks. Each peer can store data locally and define relationships between its data and the data provided by other peers. Queries posed to any of the peers are then answered by also considering the information implied by those mappings. The overall goal of PDM is to provide semantically well-founded integration and exchange of heterogeneous and distributed data sources. Unlike traditional data integration systems, peer data management systems (PDMSs) thereby allow for full autonomy of each member and need no central coordinator. The promise of such systems is to provide flexible data integration and exchange at low setup and maintenance costs. However, building such systems raises many challenges. Beside the obvious scalability problem, choosing an appropriate semantics that can deal with arbitrary, even cyclic topologies, data inconsistencies, or updates while at the same time allowing for tractable reasoning has been an area of active research in the last decade. In this survey we provide an overview of the different approaches suggested in the literature to tackle these problems, focusing on appropriate semantics for query answering and data exchange rather than on implementation specific problems

The Complexity of Social Coordination

Coordination is a challenging everyday task; just think of the last time you organized a party or a meeting involving several people. As a growing part of our social and professional life goes online, an opportunity for an improved coordination process arises. Recently, Gupta et al. proposed entangled queries as a declarative abstraction for data-driven coordination, where the difficulty of the coordination task is shifted from the user to the database. Unfortunately, evaluating entangled queries is very hard, and thus previous work considered only a restricted class of queries that satisfy safety (the coordination partners are fixed) and uniqueness (all queries need to be satisfied). In this paper we significantly extend the class of feasible entangled queries beyond uniqueness and safety. First, we show that we can simply drop uniqueness and still efficiently evaluate a set of safe entangled queries. Second, we show that as long as all users coordinate on the same set of attributes, we can give an efficient algorithm for coordination even if the set of queries does not satisfy safety. In an experimental evaluation we show that our algorithms are feasible for a wide spectrum of coordination scenarios.Comment: VLDB201

Making Linked Open Data Writable with Provenance Semirings

Linked Open Data cloud (LOD) is essentially read-only, re- straining the possibility of collaborative knowledge construction. To sup- port collaboration, we need to make the LOD writable. In this paper, we propose a vision for a writable linked data where each LOD participant can define updatable materialized views from data hosted by other par- ticipants. Consequently, building a writable LOD can be reduced to the problem of SPARQL self-maintenance of Select-Union recursive mate- rialized views. We propose TM-Graph, an RDF-Graph annotated with elements of a specialized provenance semiring to maintain consistency of these views and we analyze complexity in space and traffic

AcCORD: um modelo colaborativo assíncrono para a reconciliação de dados

Reconciliation is the process of providing a consistent view of the data imported from different sources. Despite some efforts reported in the literature for providing data reconciliation solutions with asynchronous collaboration, the challenge of reconciling data when multiple users work asyn- chronously over local copies of the same imported data has received less attention. In this thesis we investigate this challenge. We propose AcCORD, an asynchronous collaborative data reconciliation model. It stores users’ integration decision in logs, called repositories. Repositories keep data prove- nance, that is, the operations applied to the data sources that led to the current state of the data. Each user has her own repository for storing the provenance. That is, whenever inconsistencies among im- ported sources are detected, the user may autonomously take decisions to solve them, and integration decisions that are locally executed are registered in her repository. Integration decisions are shared among collaborators by importing each other’s repositories. Since users may have different points of view, repositories may also be inconsistent. Therefore, AcCORD also introduces several policies that can be applied by different users in order to solve conflicts among repositories and reconcile their integration decisions. Depending on the applied policy, the final view of the imported sources may either be the same for all users, that is, a single integrated view, or result in distinct local views for each of them. Furthermore, AcCORD encompasses a decision integration propagation method, which is aimed to avoid that a user take inconsistent decisions over the same data conflict present in different sources, thus guaranteeing a more effective reconciliation process. AcCORD was validated through performance tests that investigated the proposed policies and through users’ interviews that investigated not only the proposed policies but also the quality of the multiuser reconciliation. The re- sults demonstrated the efficiency and efficacy of AcCORD, and highlighted its flexibility to generate a single integrated view or different local views. The interviews demonstrated different perceptions of the users with regard to the quality of the result provided by AcCORD, including aspects related to consistency, acceptability, correctness, time-saving and satisfaction.Reconciliação é o processo de prover uma visão consistente de dados provenientes de várias fontes de dados. Embora existam na literatura trabalhos voltados à proposta de soluções de reconciliação baseadas em colaboração assíncrona, o desafio de reconciliar dados quando vários usuários colaborativos trabalham de forma assíncrona sobre as mesmas co´pias locais de dados, compartilhando somente eventualmente as suas decisões de integração particulares, tem recebido menos atenção. Nesta tese de doutorado investiga-se esse desafio, por meio da proposta do modelo AcCORD (Asynchronous COllaborative data ReconcIliation moDel). AcCORD é um modelo colaborativo assíncrono para reconciliação de dados no qual as atualizações dos usuários são mantidas em um repositório de operações na forma de dados de procedência. Cada usuário tem o seu próprio repositório para armazenar a procedência e a sua própria cópia das fontes. Ou seja, quando inconsistências entre fontes importadas são detectadas, o usuário pode tomar decisões de integração para resolvê-las de maneira autônoma, e as atualizações que são executadas localmente são registradas em seu próprio repositório. As atualizações são compartilhadas entre colaboradores quando um usuário importa as operações dos repositórios dos demais usuários. Desde que diferentes usuários podem ter diferentes pontos de vista para resolver o mesmo conflito, seus repositórios podem estar inconsistentes. Assim, o modelo Ac- CORD também inclui a proposta de diferentes políticas de reconciliação multiusuário para resolver conflitos entre repositórios. Políticas distintas podem ser aplicadas por diferentes usuários para reconciliar as suas atualizações. Dependendo da política aplicada, a visão final das fontes importadas pode ser a mesma para todos os usuários, ou seja, um única visão global integrada, ou resultar em distintas visões locais para cada um deles. Adicionalmente, o modelo AcCORD também incorpora um método de propagação de decisões de integração, o qual tem como objetivo evitar que um usuário tome decisões inconsistentes a respeito de um mesmo conflito de dado presente em diferentes fontes, garantindo um processo de reconciliação multiusuário mais efetivo. O modelo AcCORD foi validado por meio de testes de desempenho que avaliaram as políticas propostas, e por entrevistas a usuários que avaliaram não somente as políticas propostas mas também a qualidade da reconciliação multiusuário. Os resultados obtidos demonstraram a eficiência e a eficácia do modelo proposto, além de sua flexibilidade para gerar uma visão integrada ou distintas visões locais. As entrevistas realizadas demonstraram diferentes percepções dos usuários quanto à qualidade do resultado provido pelo modelo AcCORD, incluindo aspectos relacionados à consistência, aceitabilidade, corretude, economia de tempo e satisfacão

Investigation and development of a tangible technology framework for highly complex and abstract concepts

The ubiquitous integration of computer-supported learning tools within the educational domain has led educators to continuously seek effective technological platforms for teaching and learning. Overcoming the inherent limitations of traditional educational approaches, interactive and tangible computing platforms have consequently garnered increased interest in the pursuit of embedding active learning pedagogies within curricula. However, whilst Tangible User Interface (TUI) systems have been successfully developed to edutain children in various research contexts, TUI architectures have seen limited deployment towards more advanced educational pursuits. Thus, in contrast to current domain research, this study investigates the effectiveness and suitability of adopting TUI systems for enhancing the learning experience of abstract and complex computational science and technology-based concepts within higher educational institutions (HEI)s. Based on the proposal of a contextually apt TUI architecture, the research describes the design and development of eight distinct TUI frameworks embodying innovate interactive paradigms through tabletop peripherals, graphical design factors, and active tangible manipulatives. These computationally coupled design elements are evaluated through summative and formative experimental methodologies for their ability to aid in the effective teaching and learning of diverse threshold concepts experienced in computational science. In addition, through the design and adoption of a technology acceptance model for educational technology (TAM4Edu), the suitability of TUI frameworks in HEI education is empirically evaluated across a myriad of determinants for modelling students’ behavioural intention. In light of the statistically significant results obtained in both academic knowledge gain (μ = 25.8%) and student satisfaction (μ = 12.7%), the study outlines the affordances provided through TUI design for various constituents of active learning theories and modalities. Thus, based on an empirical and pedagogical analyses, a set of design guidelines is defined within this research to direct the effective development of TUI design elements for teaching and learning abstract threshold concepts in HEI adaptations

Tabletop tangible maps and diagrams for visually impaired users

En dépit de leur omniprésence et de leur rôle essentiel dans nos vies professionnelles et personnelles, les représentations graphiques, qu'elles soient numériques ou sur papier, ne sont pas accessibles aux personnes déficientes visuelles car elles ne fournissent pas d'informations tactiles. Par ailleurs, les inégalités d'accès à ces représentations ne cessent de s'accroître ; grâce au développement de représentations graphiques dynamiques et disponibles en ligne, les personnes voyantes peuvent non seulement accéder à de grandes quantités de données, mais aussi interagir avec ces données par le biais de fonctionnalités avancées (changement d'échelle, sélection des données à afficher, etc.). En revanche, pour les personnes déficientes visuelles, les techniques actuellement utilisées pour rendre accessibles les cartes et les diagrammes nécessitent l'intervention de spécialistes et ne permettent pas la création de représentations interactives. Cependant, les récentes avancées dans le domaine de l'adaptation automatique de contenus laissent entrevoir, dans les prochaines années, une augmentation de la quantité de contenus adaptés. Cette augmentation doit aller de pair avec le développement de dispositifs utilisables et abordables en mesure de supporter l'affichage de représentations interactives et rapidement modifiables, tout en étant accessibles aux personnes déficientes visuelles. Certains prototypes de recherche s'appuient sur une représentation numérique seulement : ils peuvent être instantanément modifiés mais ne fournissent que très peu de retour tactile, ce qui rend leur exploration complexe d'un point de vue cognitif et impose de fortes contraintes sur le contenu. D'autres prototypes s'appuient sur une représentation numérique et physique : bien qu'ils puissent être explorés tactilement, ce qui est un réel avantage, ils nécessitent un support tactile qui empêche toute modification rapide. Quant aux dispositifs similaires à des tablettes Braille, mais avec des milliers de picots, leur coût est prohibitif. L'objectif de cette thèse est de pallier les limitations de ces approches en étudiant comment développer des cartes et diagrammes interactifs physiques, modifiables et abordables. Pour cela, nous nous appuyons sur un type d'interface qui a rarement été étudié pour des utilisateurs déficients visuels : les interfaces tangibles, et plus particulièrement les interfaces tangibles sur table. Dans ces interfaces, des objets physiques représentent des informations numériques et peuvent être manipulés par l'utilisateur pour interagir avec le système, ou par le système lui-même pour refléter un changement du modèle numérique - on parle alors d'interfaces tangibles sur tables animées, ou actuated. Grâce à la conception, au développement et à l'évaluation de trois interfaces tangibles sur table (les Tangible Reels, la Tangible Box et BotMap), nous proposons un ensemble de solutions techniques répondant aux spécificités des interfaces tangibles pour des personnes déficientes visuelles, ainsi que de nouvelles techniques d'interaction non-visuelles, notamment pour la reconstruction d'une carte ou d'un diagramme et l'exploration de cartes de type " Pan & Zoom ". D'un point de vue théorique, nous proposons aussi une nouvelle classification pour les dispositifs interactifs accessibles.Despite their omnipresence and essential role in our everyday lives, online and printed graphical representations are inaccessible to visually impaired people because they cannot be explored using the sense of touch. The gap between sighted and visually impaired people's access to graphical representations is constantly growing due to the increasing development and availability of online and dynamic representations that not only give sighted people the opportunity to access large amounts of data, but also to interact with them using advanced functionalities such as panning, zooming and filtering. In contrast, the techniques currently used to make maps and diagrams accessible to visually impaired people require the intervention of tactile graphics specialists and result in non-interactive tactile representations. However, based on recent advances in the automatic production of content, we can expect in the coming years a growth in the availability of adapted content, which must go hand-in-hand with the development of affordable and usable devices. In particular, these devices should make full use of visually impaired users' perceptual capacities and support the display of interactive and updatable representations. A number of research prototypes have already been developed. Some rely on digital representation only, and although they have the great advantage of being instantly updatable, they provide very limited tactile feedback, which makes their exploration cognitively demanding and imposes heavy restrictions on content. On the other hand, most prototypes that rely on digital and physical representations allow for a two-handed exploration that is both natural and efficient at retrieving and encoding spatial information, but they are physically limited by the use of a tactile overlay, making them impossible to update. Other alternatives are either extremely expensive (e.g. braille tablets) or offer a slow and limited way to update the representation (e.g. maps that are 3D-printed based on users' inputs). In this thesis, we propose to bridge the gap between these two approaches by investigating how to develop physical interactive maps and diagrams that support two-handed exploration, while at the same time being updatable and affordable. To do so, we build on previous research on Tangible User Interfaces (TUI) and particularly on (actuated) tabletop TUIs, two fields of research that have surprisingly received very little interest concerning visually impaired users. Based on the design, implementation and evaluation of three tabletop TUIs (the Tangible Reels, the Tangible Box and BotMap), we propose innovative non-visual interaction techniques and technical solutions that will hopefully serve as a basis for the design of future TUIs for visually impaired users, and encourage their development and use. We investigate how tangible maps and diagrams can support various tasks, ranging from the (re)construction of diagrams to the exploration of maps by panning and zooming. From a theoretical perspective we contribute to the research on accessible graphical representations by highlighting how research on maps can feed research on diagrams and vice-versa. We also propose a classification and comparison of existing prototypes to deliver a structured overview of current research