A visual multivariate dynamic egocentric network exploration tool

Visualizing multivariate dynamic networks is a challenging task. The evolution of the dynamic network within the temporal axis must be depicted in conjunction with the associated multivariate attributes. In this thesis, an exploratory visual analytics tool is proposed to display multivariate dynamic networks with spatial attributes. The proposed tool displays the distribution of multivariate temporal domain and network attributes in scattered views. Moreover, in order to expose the evolution of a single or a group of nodes in the dynamic network along the temporal axis, an egocentric approach is applied in which a node is represented with its neighborhood as an ego-network. This approach allows users to observe a node's surrounding environment along the temporal axis. On top of the traditional ego-network visualization methods, such as timelines, the proposed tool encodes ego-networks as feature vectors consisting of the domain and network attributes and projects them onto 2D views. As a result, distances between projected ego-networks represent the dissimilarity across temporal axis in a single view. The proposed tool is demonstrated with a real-world use case scenario on merchant networks obtained from a one-year long credit card transaction

VisForum: A visual analysis system for exploring user groups in online forums

User grouping in asynchronous online forums is a common phenomenon nowadays. People with similar backgrounds or shared interests like to get together in group discussions. As tens of thousands of archived conversational posts accumulate, challenges emerge for forum administrators and analysts to effectively explore user groups in large-volume threads and gain meaningful insights into the hierarchical discussions. Identifying and comparing groups in discussion threads are nontrivial, since the number of users and posts increases with time and noises may hamper the detection of user groups. Researchers in data mining fields have proposed a large body of algorithms to explore user grouping. However, the mining result is not intuitive to understand and difficult for users to explore the details. To address these issues, we present VisForum, a visual analytic system allowing people to interactively explore user groups in a forum. We work closely with two educators who have released courses in Massive Open Online Courses (MOOC) platforms to compile a list of design goals to guide our design. Then, we design and implement a multi-coordinated interface as well as several novel glyphs, i.e., group glyph, user glyph, and set glyph, with different granularities. Accordingly, we propose the group Detecting 8 Sorting Algorithm to reduce noises in a collection of posts, and employ the concept of “forum-index” for users to identify high-impact forum members. Two case studies using real-world datasets demonstrate the usefulness of the system and the effectiveness of novel glyph designs. Furthermore, we conduct an in-lab user study to present the usability of VisForum.</jats:p

Visualização de mobilidade e multihoming em redes sem fios

Engenharia Eletrónica e TelecomunicaçõesNos últimos anos, as pessoas têm-se tornado cada vez mais dependentes do uso de dispositivos móveis pessoais. Desta forma, tornouse indispensável fornecer acesso à Internet aos dispositivos dos utilizadores, em qualquer lugar e em qualquer altura. Estes utilizadores estão em constante movimento, logo a mobilidade apresenta um fator chave nas comunicações nos dias de hoje. A utilização de Hostmultihoming permite que os dispositivos dos utilizadores, que possuam várias interfaces de rede, passam estar ligados simultaneamente a várias redes de acesso. Com esta abordagem é possível aproveitar melhor os recursos que se encontram ao alcance do utilizador e fornecer uma ligação mais fiável. Com a integração de mobilidade e multihoming em redes sem fios é possível satisfazer as exigências cada vez mais elevadas dos utilizadores e oferecer uma melhor experiência de utilização. Com estes mecanismos implementados na rede é agora importante apresentar as suas características e funcionalidades. A forma mais intuitiva e interessante de perceber as mudanças que ocorrem na rede é através de uma plataforma de visualização. Para demonstrar as funcionalidades é necessário interagir com os nós da rede e despoletar remotamente eventos na rede. Estes eventos também devem ser visualizados de modo a perceber as mudanças que ocorrem na rede. O objetivo desta dissertação é desenvolver uma plataforma de visualização capaz de visualizar mobilidade e multihoming na rede, e interagir com a rede para despoletar remotamente eventos na mesma. Para atingir este objetivo, desenvolveu-se e integrou-se uma framework num protocolo de mobilidade com suporte para multihoming. De forma a demonstrar as funcionalidades da plataforma desenvolvida, implementaram-se duas testbeds em ambiente laboratorial, e de seguida realizaram-se testes para verificar as funcionalidades implementadas e o seu desempenho.In the last years we have witnessed that people are becoming increasingly dependent on the use of personal mobile devices. Providing Internet access to users’ devices while maintaining Quality-of-service has become indispensable. The users are constantly moving, and mobility presents a key factor in today’s communications. Host-multihoming allows end-user devices equipped with multiple network interfaces to be simultaneously connected to multiple access networks. This can optimally leverage the resources that are in the range of the end-user device and provide a greater sense of connection reliability. Implementing both mobility and multihoming in wireless networks can accommodate the increasing demands of the users and provide better user experience and network utilization. When these mechanisms are implemented in the network, it is important to present their features and demonstrate their functionalities. Visualization provides an intuitive and interesting way of understanding the changes that occur in the network. In order to demonstrate the functionalities, it is necessary to interact with the network nodes and remotely trigger network actions. These actions should also be visualized to understand the changes that happened in the network. The objective of this Dissertation is to develop a visualization platform able both to visualize mobility and multihoming in the network, and interact with the network to remotely trigger network actions. For this purpose, a framework has been developed and integrated in a mobility protocol with multihoming support. To demonstrate the functionalities of the developed platform, a testbed has been deployed in the laboratory environment and tests were performed to verify the implemented functionalities and evaluate its performance. The results show that the platform is able to visualize both mobility and multihoming in real-time. Also, the platform can interact with the network nodes in order to trigger network related actions, and visualize the result of these actions

The state of the art in empirical user evaluation of graph visualizations

While graph drawing focuses more on the aesthetic representation of node-link diagrams, graph visualization takes into account other visual metaphors making them useful for graph exploration tasks in information visualization and visual analytics. Although there are aesthetic graph drawing criteria that describe how a graph should be presented to make it faster and more reliably explorable, many controlled and uncontrolled empirical user studies flourished over the past years. The goal of them is to uncover how well the human user performs graph-specific tasks, in many cases compared to previously designed graph visualizations. Due to the fact that many parameters in a graph dataset as well as the visual representation of them might be varied and many user studies have been conducted in this space, a state-of-the-art survey is needed to understand evaluation results and findings to inform the future design, research, and application of graph visualizations. In this paper, we classify the present literature on the topmost level into graph interpretation, graph memorability, and graph creation where the users with their tasks stand in focus of the evaluation not the computational aspects. As another outcome of this work, we identify the white spots in this field and sketch ideas for future research directions

Neural Encoding of Local vs. Global Space: From Structure to Function

The retrosplenial cortex may be important for navigating visually similar compartmentalised spaces by conjunctively encoding both local and global environments. Previously, a novel directional signal that encodes local spaces was found in the dysgranular retrosplenial cortex (dRSC) while global head direction encoding was found in both dRSC and granular retrosplenial cortex (gRSC; Jacob et al., 2017). This thesis addresses two questions arising from this finding: (i) how does the local directional signal arise? and (ii) do the downstream place cells (cells that display spatially constrained firing) display local or global encoding? The first question was explored by retrogradely labelling the neuronal inputs into the two retrosplenial regions under the hypothesis that the differences in directional encoding are due to differences in their inputs. Particularly, gRSC was found to receive more inputs from anterodorsal thalamus, which was previously shown to display global encoding (Jacob et al., 2017). In addition, gRSC, but not dRSC, received inputs from dorsal subiculum which is the main output structure of hippocampus. It is however unclear if place cell in hippocampus displayed local or global place encoding. The second question thus arises: Do place cells display local or global place encoding? As hippocampus is strongly coupled with gRSC, place cells were predicted to show a global representation similar to that in gRSC. Extracellular recording of place cells in an environment with two differentially scented, visually rotated compartments showed that no place cells that are sensitive to the local visual scene were found. Thus, place cells displayed global encoding. Together, these findings indicate that global encoding in gRSC may be a consequence of its stronger coupling with vestibular-directional nuclei and the hippocampal system, both of which displayed global encoding. In contrast, the local encoding observed in dRSC may reflect its structural disconnect from the global spatial network

Tasks and visual techniques for the exploration of temporal graph data

This thesis considers the tasks involved in exploratory analysis of temporal graph data, and the visual techniques which are able to support these tasks. There has been an enormous increase in the amount and availability of graph (network) data, and in particular, graph data that is changing over time. Understanding the mechanisms involved in temporal change in a graph is of interest to a wide range of disciplines. While the application domain may differ, many of the underlying questions regarding the properties of the graph and mechanism of change are the same.The research area of temporal graph visualisation seeks to address the challenges involved in visually representing change in a graph over time. While most graph visualisation tools focus on static networks, recent research has been directed toward the development of temporal visualisation systems. By representing data using computer-generated graphical forms, Information Visualisation techniques harness human perceptual capabilities to recognise patterns, spot anomalies and outliers, and find relationships within the data. Interacting with these graphical representations allow individuals to explore large datasets and gain further insightinto the relationships between different aspects of the data. Visual approaches are particularly relevant for Exploratory Data Analysis (EDA), where the person performing the analysis may be unfamiliar with the data set, and their goal is to make new discoveries and gain insight through its exploration. However, designing visual systems for EDA can be difficult, as the tasks which a person may wish to carry out during their analysis are not always known at outset. Identifying and understanding the tasks involved in such a process has given rise to a number of task taxonomies which seek to elucidate the tasks and structure them in a useful way.While task taxonomies for static graph analysis exist, no suitable temporal graph taxonomy has yet been developed. The first part of this thesis focusses on the development of such a taxonomy. Through the extension and instantiation of an existing formal task framework for general EDA, a task taxonomy and a task design space are developed specifically for exploration of temporal graph data. The resultant task framework is evaluated with respect to extant classifications and is shown to address a number of deficiencies in task coverage in existing works. Its usefulness in both the design and evaluation processes is also demonstrated.Much research currently surrounds the development of systems and techniques for visual exploration of temporal graphs, but little is known about how the different types of techniques relate to one another and which tasks they are able to support. The second part of this thesis focusses on the possibilities in this area: a design spaceof the possible visual encodings for temporal graph data is developed, and extant techniques are classified into this space, revealing potential combinations of encodings which have not yet been employed. These may prove interesting opportunities for further research and the development of novel techniques.The third part of this work addresses the need to understand the types of analysis the different visual techniques support, and indeed whether new techniques are required. The techniques which are able to support the different task dimensions are considered. This task-technique mapping reveals that visual exploration of temporalgraph data requires techniques not only from temporal graph visualisation, but also from static graph visualisation and comparison, and temporal visualisation. A number of tasks which are unsupported or less-well supported, which could prove interesting opportunities for future research, are identified.The taxonomies, design spaces, and mappings in this work bring order to the range of potential tasks of interest when exploring temporal graph data and the assortmentof techniques developed to visualise this type of data, and are designed to be of use in both the design and evaluation of temporal graph visualisation systems