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Journal of Visual Languages & Computing 25

Editors:S.-K. Chang
Standard No:ISSN: 1045-926X
Links:Table of Contents
  1. VLC 2014-02 Volume 25 Issue 1
  2. VLC 2014-04 Volume 25 Issue 2
  3. VLC 2014-06 Volume 25 Issue 3
  4. VLC 2014-08 Volume 25 Issue 4
  5. VLC 2014-10 Volume 25 Issue 5

VLC 2014-02 Volume 25 Issue 1

Guest Co-Editor's Introduction BIBFull-Text 1
  Wei Lu; Weiwei Xing
A conceptual framework for geographic knowledge engineering BIBAKFull-Text 2-19
  Robert Laurini
In many applications, the management of geographic knowledge is very important especially not only for urban and environmental planning, but also for any application in territorial intelligence. However there are several practical problems hindering the efficiency, some of them being technical and other being more conceptual. The goal of this paper is to present a tentative conceptual framework for managing practical geographic knowledge taking account of accuracy, rotundity of earth, the mobility of objects, multiple-representation, multi-scale, existence of sliver polygons, differences in classifying real features (ontologies), the many-to-many relationship of place names (gazetteers) and the necessity of interoperability. In other words, this framework must be robust against scaling, generalization and small measurement errors. Therefore, geographic objects must be distinguished into several classes of objects with different properties, namely geodetic objects, administrative objects, manmade objects and natural objects. Regarding spatial relations, in addition to conventional topological and projective relations, other relations including tessellations and ribbon topology relations are presented in order to help model geographic objects by integrating more practical semantics. Any conceptual framework is based on principles which are overall guidelines and rules; moreover, principles allow at making predictions and drawing implications and are finally the basic building blocks of theoretical models. But before identifying the principles, one needs some preliminary considerations named prolegomena. In our case, principles will be essentially rules for transforming geographic knowledge whereas prolegomena will be assertions regarding more the foundations of geographic science. Based on those considerations, 12 principles are given, preceded by 12 prolegomena. For instance, some principles deal with the transformation of spatial relationships based on visual acuity and granularity of interest, with the influence of neighboring information and cross-boundary interoperability. New categories of geographic knowledge types are presented, spatial facts, cluster of areas, flows of persons, goods, etc., topological constraints and co-location rules. To represent knowledge chunks, three styles are presented, based respectively on descriptive logics, XML and visual languages. To conclude this paper, after having defined contexts of interpretation, an example of visual language to manage geographic knowledge is proposed.
Keywords: Geoprocessing fundamentals; Geographic knowledge engineering; Spatial knowledge engineering; Visual language; Geographic reasoning
Hybrid motion graph for character motion synthesis BIBAKFull-Text 20-32
  Weiwei Xing; Xiang Wei; Jian Zhang; Cheng Ren; Wei Lu
Objective: This paper proposes a novel framework of Hybrid Motion Graph (HMG) for creating character animations, which enhances the graph-based structural control by motion field representations for efficient motion synthesis of diverse and interactive character animations.
   Methods: In HMG framework, the motion template of each class is automatically derived from the training motions for capturing the general spatio-temporal characteristics of an entire motion class. Typical motion field for each class is then constructed. The smooth transitions among motion classes are then generated by interpolating the related motion templates with spacetime constraints. Finally, a hybrid motion graph is built by integrating the separate motion fields for each motion class into the global structural control of motion graph through smooth transition.
   Results: In motion synthesis stage, a character may freely 'switch' among different motion classes in the hybrid motion graph via smooth transitions between motion templates and 'flow' within each class through the continuous space of motion field with agile and the continuous control process.
   Conclusion: Experimental results show that our framework realizes the fast connectivity among different motion classes and high responsiveness and interactivity for creating realistic character animation of rich behaviors with limited motion data and computational resources.
Keywords: Motion synthesis; Motion graph; Motion fields; Motion template; Motion transition
A new approach for inner-knuckle-print recognition BIBAKFull-Text 33-42
  Ming Liu; Yongmei Tian; Li Lihua
Objective: This paper proposed a new approach for inner-knuckle-print (IKP) recognition. In traditional IKP recognition systems, the region of interest (ROI) is extracted from the image of the whole hand and the directions of the fingers being imaged are not restricted. The result maybe incorrect because that the shape and surface of the fingers may vary greatly. Moreover, if the direction of the finger being imaged is not restricted, there may be severe rotation transform between intra-class IKPs. To overcome these drawbacks, we develop a new data acquisition scheme as well as an efficient personal authentication algorithm.
   Methods: The new scheme is designed to capture the image of the inner surface of the middle knuckles of the middle and ring fingers. The fingers being imaged are kept horizontal with two pegs, so that the rotation angle between different images obtained from the same hand can be minimized. The new personal authentication algorithm consists of the next four steps. Firstly, two regions of interest (ROI), each of which contains the inner surface of a knuckle, are cropped from the original image. Secondly, line features are extracted from the ROIs based on the combination of Gabor filtering and derivative line detection method. Then, binary line images are matched by using a cross-correlation-based method. Finally, the input data is classified through score level fusion.
   Results: To evaluate the proposed IKP recognition system, a finger image database which includes 2000 images from 100 volunteers is established. The images are captured on two separate occasions, at an interval of around two months. Most of the volunteers are not familiar with the image acquisition process. The experimental results show that the proposed system achieves high recognition rate and it works in real time. Moreover, the proposed line feature extraction method outperforms traditional Gabor filter based line detection method and derivative line detection method in accuracy.
   Conclusion: The proposed IKP system is robust and accurate. It may promote the application and popularization of IKP recognition.
Keywords: Biometrics; Personal authentication; Inner-knuckle-print; Image matching
Learning motion patterns in unstructured scene based on latent structural information BIBAKFull-Text 43-53
  Weibin Liu; Xinyi Chong; Pengfei Huang; Norman I. Badler
Context: As trajectory analysis is widely used in the fields of video surveillance, crowd monitoring, behavioral prediction, and anomaly detection, finding motion patterns is a fundamental task for pedestrian trajectory analysis. Objective: In this paper, we focus on learning dominant motion patterns in unstructured scene.
   Methods: As the invisible implicit indicator to scene structure, latent structural information is first defined and learned by clustering source/sink points using CURE algorithm. Considering the basic assumption that most pedestrians would find the similar paths to pass through an unstructured scene if their entry and exit areas are fixed, trajectories are then grouped based on the latent structural information. Finally, the motion patterns are learned for each group, which are characterized by a series of statistical temporal and spatial properties including length, duration and envelopes in polar coordinate space.
   Results: Experimental results demonstrate the feasibility and effectiveness of our method, and the learned motion patterns can efficiently describe the statistical spatiotemporal models of the typical pedestrian behaviors in a real scene. Based on the learned motion patterns, abnormal or suspicious trajectories are detected.
   Conclusion: The performance of our approach shows high spatial accuracy and low computational cost.
Keywords: Crowd analysis; Motion pattern; Latent structural information; Anomaly detection

VLC 2014-04 Volume 25 Issue 2

Special issue on diagram aesthetics and layout: Guest editors' introduction BIBFull-Text 55-56
  Beryl Plimmer; Peter Rodgers; Gem Stapleton
Twelve years of diagrams research BIBAKFull-Text 57-75
  Helen C. Purchase
Research into the use of diagrams is an interdisciplinary endeavour, encompassing disciplines as diverse as psychology, architecture and artificial intelligence. It is also a relatively new research area, with the first meeting of like-minded researchers interested in studying diagrams taking place in 1997. Now that diagrams research is more established, it is timely to review its scope, nature and progress. This paper reviews diagrams research over the past twelve years, as represented in the proceedings of the International Conference on the Theory and Application of Diagrams. In summarising the contents of these proceedings, a taxonomy describing the scope of diagrams research is proposed, the several research issues covered are identified, and the extent to which layout and aesthetics form part of this body of research is discussed. In concluding, trends and under-represented areas are noted and discussed. The aim of the paper is not only to summarise the research covered in this particular conference, but to provide a basis for on-going discussion on the changing nature of diagrams research.
Keywords: Diagrams research; Diagrams classifications; Interdisciplinary research; Literature survey
Towards a systematic understanding of graphical cues in communication through statistical graphs BIBAKFull-Text 76-88
  Cengiz Acartürk
Statistical graphs -- in particular, line graphs and bar graphs -- are efficient means of communication in a wide range of non-expert settings. In communication settings, statistical graphs do not only serve as visualizations of individual data points but also provide visual access to various aspects of the information contained in data. Moreover, specific types of graphs are better means for providing visual access to certain aspects of data. For instance, trend information is visually conveyed through line graphs and bar graphs in the time domain. The interpretation of the information content in a graph is influenced by several factors, such as perceptual salience of line segments in a line graph. In addition, the presence of graphical cues substantially influences the interpretation of graph readers. Graphical cues are visual elements, usually in the form of point markers, non-directional lines, curves and arrows. They play a communicative role in communication through graphs. The present study reports an experimental investigation, in which the participants provided verbal descriptions of a set of graphs with/without graphical cues. The stimuli involved line graphs and bar graphs that represented the same data. The analyses of eye movements and verbal protocols reveal that the interpretations of the participants are systematically influenced by the presence or absence of a graphical cue, the type of the graphical cue (i.e., a point marker vs. an arrow), as well as the type of the graph (i.e., a line graph vs. a bar graph).
Keywords: Statistical graphs; Line graphs; Bar graphs; Graphical cues; Verbal protocols; Eye movements
Drawing layered graphs with port constraints BIBAKFull-Text 89-106
  Christoph Daniel Schulze; Miro Spönemann; Reinhard von Hanxleden
Complex software systems are often modeled using data flow diagrams, in which nodes are connected to each other through dedicated connection points called ports. The influence a layout algorithm has on the placement of ports is determined by port constraints defined on the corresponding node.
   In this paper we present approaches for integrating port constraints into the layer-based approach to graph drawing pioneered by Sugiyama et al. We show how our layout algorithm, called KLay Layered, progresses from relaxed to more restricted port constraint levels as it executes, and how established algorithms for crossing minimization and edge routing can be extended to support port constraints. Compared to the previous layout algorithms supporting ports, our algorithm produces fewer edge crossings and bends and yields pleasing results.
   We also explain and evaluate how layout algorithms can be kept simple by using the concept of intermediate processors to structure them in a modular way. A case study integrating our layout algorithm into UC Berkeley's Ptolemy tool illustrates how KLay Layered can be integrated into Java-based applications.
Keywords: Graph drawing; Crossing minimization; Port constraints; Layered graphs; Data flow diagrams
Would you prefer pie or cupcakes? Preferences for data visualization designs of professionals and laypeople in graphic design BIBAKFull-Text 107-116
  Annemarie Quispel; Alfons Maes
Data visualizations come in many different forms. In this study we investigated how professionals and laypeople in graphic design rate the attractiveness and clarity of data visualizations differing in construction type (standard or non-standard) and mode of expression (pictorial or abstract). Results showed that graphic designers rate the attractiveness of non-standard and pictorial visualizations higher than standard and abstract ones, whereas the opposite is true for laypeople. As for clarity, both groups prefer standard and abstract visualizations, which is reflected in lower response times. Results also showed that overall graphic designers' evaluations are lower than the evaluations of laypeople.
Keywords: Data visualization; Aesthetics; Layout; Graphic design
A linear time layout algorithm for business process models BIBAKFull-Text 117-132
  Thomas Gschwind; Jakob Pinggera; Stefan Zugal; Hajo A. Reijers; Barbara Weber
The layout of a business process model influences how easily it can be understood. Existing layout features in process modeling tools often rely on graph representations, but do not take the specific properties of business process models into account. In this paper, we propose an algorithm that is based on a set of constraints which are specifically identified toward establishing a readable layout of a process model. Our algorithm exploits the structure of the process model and allows the computation of the final layout in linear time. We explain the algorithm, show its detailed run-time complexity, compare it to existing algorithms, and demonstrate in an empirical evaluation the acceptance of the layout generated by the algorithm. The data suggests that the proposed algorithm is well perceived by moderately experienced process modelers, both in terms of its usefulness as well as its ease of use.
Keywords: Layout; Graph; Workflow; Workflow languages; Business process model

VLC 2014-06 Volume 25 Issue 3

Special Issue: Guest Editors' Introduction BIBFull-Text 133
  Peter Chapman; Luana Micallef
A survey of Euler diagrams BIBAKFull-Text 134-155
  Peter Rodgers
Euler diagrams visually represent containment, intersection and exclusion using closed curves. They first appeared several hundred years ago, however, there has been a resurgence in Euler diagram research in the twenty-first century. This was initially driven by their use in visual languages, where they can be used to represent logical expressions diagrammatically. This work lead to the requirement to automatically generate Euler diagrams from an abstract description. The ability to generate diagrams has accelerated their use in information visualization, both in the standard case where multiple grouping of data items inside curves is required and in the area-proportional case where the area of curve intersections is important. As a result, examining the usability of Euler diagrams has become an important aspect of this research. Usability has been investigated by empirical studies, but much research has concentrated on wellformedness, which concerns how curves and other features of the diagram interrelate. This work has revealed the drawability of Euler diagrams under various wellformedness properties and has developed embedding methods that meet these properties.
   Euler diagram research surveyed in this paper includes theoretical results, generation techniques, transformation methods and the development of automated reasoning systems for Euler diagrams. It also overviews application areas and the ways in which Euler diagrams have been extended.
Keywords: Euler diagrams
Towards explaining the cognitive efficacy of Euler diagrams in syllogistic reasoning: A relational perspective BIBAKFull-Text 156-169
  Koji Mineshima; Yuri Sato; Ryo Takemura; Mitsuhiro Okada
Although diagrams have been widely used as methods for introducing students to elementary logical reasoning, it is still open to debate in cognitive psychology whether logic diagrams can aid untrained people to successfully conduct deductive reasoning. In our previous work, some empirical evidence was provided for the effectiveness of Euler diagrams in the process of solving categorical syllogisms. In this paper, we discuss the question of why Euler diagrams have such inferential efficacy in the light of a logical and proof-theoretical analysis of categorical syllogisms and diagrammatic reasoning. As a step towards an explanatory theory of reasoning with Euler diagrams, we argue that the effectiveness of Euler diagrams in supporting syllogistic reasoning derives from the fact that they are effective ways of representing and reasoning about relational structures that are implicit in categorical sentences. A special attention is paid to how Euler diagrams can facilitate the task of checking the invalidity of an inference, a task that is known to be particularly difficult for untrained reasoners. The distinctive features of our conception of diagrammatic reasoning are made clear by comparing it with the model-theoretic conception of ordinary reasoning developed in the mental model theory.
Keywords: Diagrammatic reasoning; Euler diagram; Efficacy; Categorical syllogisms; Relational inferences; Mental model theory
Graphical notations for syllogisms: How alternative representations impact the accessibility of concepts BIBAKFull-Text 170-185
  Peter C.-H. Cheng
Five notations for standard and multi-premise syllogisms are examined. Four are existing notations (verbal propositions, Euler diagrams, Venn diagrams and Englebretsen's Linear diagrams) and one a novel diagrammatic system -- Category Pattern Diagrams (CPDs). CPDs integrate spatial location, linear ordering and properties of graphical objects in a comprehensive representational format to encode information about syllogisms, which provides a contrast to the use of degrees of spatial containment in the existing diagrammatic systems. The comparison of the five notations reveals how their underlying representational schemes can substantially impact the effectiveness of the encoding of the core concepts of the knowledge domain; in particular whether the core domain concepts are readily accessible as perceptual inferences and thus the notations are semantically transparent. The relative merits of CPDs provide some support for claims about the utility of the Representational Epistemic design principles that were used to create CPDs.
Keywords: Euler diagram; Venn diagram; Linear diagram; Category Pattern Diagram; Representational format; Syllogism; Sorite; Perceptual inferences; Semantic transparency; Representational epistemology
On the drawability of 3D Venn and Euler diagrams BIBAKFull-Text 186-209
  Jean Flower; Gem Stapleton; Peter Rodgers
3D Euler diagrams visually represent the set-theoretic notions of intersection, containment and disjointness by using closed, orientable surfaces. In previous work, we introduced 3D Venn and Euler diagrams and formally defined them. In this paper, we consider the drawability of data sets using 3D Venn and Euler diagrams. The specific contributions are as follows. First, we demonstrate that there is more choice of layout when drawing 3D Euler diagrams than when drawing 2D Euler diagrams. These choices impact the topological adjacency properties of the diagrams and having more choice is helpful for some Euler diagram drawing algorithms. To illustrate this, we consider the well-known class of Venn-3 diagrams in detail. We then proceed to consider drawability questions centered around which data sets can be visualized when the diagrams are required to possess certain properties. We show that any diagram description can be drawn with 3D Euler diagrams that have unique labels. We then go on to define a set of necessary and sufficient conditions for wellformed drawability in 3D.
Keywords: Euler diagrams; Venn diagrams; 3D; Information visualization
VisualTPL: A visual dataflow language for report data transformation BIBAKFull-Text 210-226
  Woei-Kae Chen; Pin-Ying Tu
Data transformation, an important part of report generation, converts the layout of source data into a new layout suitable for presentation. Many report tools have been developed for end-users to specify data transformation. However, current report tools only support a limited set of report layouts. This paper proposes a visual dataflow programming language, called VisualTPL, to resolve this problem. Data transformation is accomplished by writing graphical dataflow programs, which manipulate tables as first-class objects with a set of extendable table operations. A report tool, called VisualTPS, has been developed to offer an easy and intuitive end-user programming environment. Reports with sophisticated layouts can be created through top-down decomposition and incremental development. An evaluation has been conducted to assess end-users' performance with VisualTPL. The results indicated that end-users could learn VisualTPL in a short time and create complicated report layouts all by themselves. And, in comparison with a commercial report tool, VisualTPL offered end-users similar performances and was preferred over the commercial tool.
Keywords: Report generation; Dataflow; Visual language; Data transformation; Table operation
A visualisation technique for large temporal social network datasets in Hyperbolic space BIBAKFull-Text 227-242
  Uraz Cengiz Turker; Selim Balcisoy
Visualisations of temporal social network datasets have the potential to be complex and require a lot of cognitive input. In this paper, we present a novel visualisation approach that depicts both relational and statistical information of evolving social structures. The underlying framework is implemented by the usage of Hyperbolic Geometry to support focus context rendering. The proposed method guarantees representing prominent social actors through scaling their representations, preserves user's mental map, and provides the user to reduce visual clutter by means of filtering.
Keywords: Social networks; Hyperbolic layout; Visualisation; Temporal data
A new visual cryptography with multi-level encoding BIBAKFull-Text 243-250
  Cheng-Chi Lee; Hong-Hao Chen; Hung-Ting Liu; Guo-Wei Chen; Chwei-Shyong Tsai
Visual secret sharing (VSS) is a visual cryptography scheme which decodes secret messages into several enlarged shares, and distributes them to different participants. The participants can recover the secret messages by stacking their shares, and then secret message can be revealed by human visual sensitivity. Afterward some researchers start to research size invariant scheme, and apply to encode grayscale images such as scenic photos or pictures, not only binary messages. Owing to the gray values distribution of pictures are different, extreme distribution may cause blurred revealed image. In this paper, we proposed a size invariant VSS scheme which is suitable for different distribution of image's gray values. Experiment results show that the reconstructed images of our method, for brighter, darker, and normal images, have clearer and higher contrast, and without apparent artifact and unexpected contour.
Keywords: Visual secret sharing; Halftone; Visual cryptography; Image; Security

VLC 2014-08 Volume 25 Issue 4

Guest editors introduction: Representations and environments for user-driven development of service applications BIBFull-Text 251-252
  Nikolay Mehandjiev; Antonella de Angeli
A visual language and environment for enterprise system modelling and automation BIBAKFull-Text 253-277
  Lei Li; John Grundy; John Hosking
Objective: We want to support enterprise service modelling and generation using a more end user-friendly metaphor than current approaches, which fail to scale to large organisations with key issues of "cobweb" and "labyrinth" problems and large numbers of hidden dependencies.
   Method: We present and evaluate an integrated visual approach for business process modelling using a novel tree-based overlay structure that effectively mitigate complexity problems. A tree-overlay based visual notation (EML) and its integrated support environment (MaramaEML) supplement and integrate with existing solutions. Complex business architectures are represented as service trees and business processes are modelled as process overlay sequences on the service trees.
   Results: MaramaEML integrates EML and BPMN to provide complementary, high-level business service modelling and supports automatic BPEL code generation from the graphical representations to realise web services implementing the specified processes. It facilitates generated service validation using an integrated LTSA checker and provides a distortion-based fisheye and zooming function to enhance complex diagram navigation. Evaluations of EML show its effectiveness.
   Conclusions: We have successfully developed and evaluated a novel tree-based metaphor for business process modelling and enterprise service generation. Practice implications: a more user-friendly modelling approach and support tool for business end users.
Keywords: Business process modelling; Web service generation; Process enactment; Zoomable user interfaces; Domain-specific visual languages; Business process modelling notation; Business process execution language
User-driven visual composition of service-based interactive spaces BIBAKFull-Text 278-296
  Carmelo Ardito; Maria Francesca Costabile; Giuseppe Desolda; Rosa Lanzilotti; Maristella Matera; Antonio Piccinno; Matteo Picozzi
Objective: The overall objective of the research work presented in this paper is to investigate models, methods and architectures to replace fixed, pre-packaged applications with flexible composition environments that make interactive environments "emerge" at run-time, based on composition actions performed by non-technical users. The approach aims at the lightweight construction of integrated, situational workspaces pervasively accessible and sharable through a variety of devices.
   Methods: Based on a meta-design approach, we designed and implemented a platform that allows end users, not necessarily experts of technologies, to extract contents from heterogeneous sources and compose Personal Information Spaces (PISs) that satisfy their information needs. Specific emphasis is posed on the adoption of a composition paradigm that abstracts from technical details and can thus be used by non-technical users.
   Results: The platform for service composition that supports the activity of the different involved stakeholders is described in details. Thanks to the separation of concerns on which the composition paradigm is based, the overall approach and its enabling platform are also amenable to customization with respect to the requirements of specific domains.
   Conclusion: We present an approach where a composition platform enables the extraction of content from heterogeneous services and its integration into situational applications where content presentation is flexibly managed through different visual templates. We also discuss the advantages offered by this approach to the stakeholders of a specific community of users in the Cultural Heritage domain.
   Practice: The developed prototypes were evaluated in laboratories and field studies: the former aimed at investigating the ease of use and the users satisfaction of the functionality and the user interface of the environment for domain customization, the latter aimed instead at observing real users (e.g., guides of an archeological park) in action, to assess the validity of the proposed composition paradigm as an EUD practice.
   Implications: The user studies described in this paper provided hints for refining the prototypes, and laid the basis for future work related to the identification of design principles that can make service-based composition technologies in general more useful and usable for end users.
Keywords: End-user development; Service composition; Personal information space; Platform-independent models
Puzzle: A mobile application development environment using a jigsaw metaphor BIBAKFull-Text 297-315
  Jose Danado; Fabio Paternò
Objective: Create a visual mobile end user development framework, named Puzzle, which allows end users without IT background to create, modify and execute applications, and provides support for interaction with smart things, phone functions and web services.
   Methods: Design of an intuitive visual metaphor and associated interaction techniques for supporting end user development in mobile devices with iterative empirical validation.
   Results: Our results show that the jigsaw is an intuitive metaphor for development in a mobile environment and our interaction techniques required a limited cognitive effort to use and learn the framework. Integration of different modalities and usage of smart things was relevant for users.
   Conclusion: Puzzle has addressed the main objective. The framework further contributes to the research on mobile end user development in order to create an incentive for users to go beyond consuming content and applications to start creating their own applications.
   Practice: Usage of a mobile end user development environment has the potential to create a shift from the conventional few-to-many distribution model of software to a many-to-many distribution model. Users will be able to create applications that fit their requirements and share their achievements with peers.
   Implications: This study has indicated that the Puzzle visual environment has the potential to enable users to easily create applications and stimulate exploration of innovative scenarios through smartphones.
Keywords: End user development; Ubiquitous computing; Mobile computing; Authoring tools; Metaphors; Interaction techniques
Analyzing topological changes for structural shape simplification BIBAKFull-Text 316-332
  Shihong Du
The shapes of regions tend to be simplified with the decrease of spatial scale or resolution, which further leads to topological changes. Analyzing topological changes is an important aspect of formalizing semantic relations. An important fact is observed that shape simplification can be considered as a combination of generalizing basic primitives. Based on this fact, a shape is decomposed first into a set of simple primitives including convexities and concavities. And then the topological changes between lines and regions can be derived from the relations between lines and primitives. The approaches presented in this study can help to analyze the exact types and locations of topological changes for generalizing convexities and concavities, respectively. The approaches need not to conduct the real simplification of shapes, and they instead incorporate the idea of simplification for deriving the changes. Thus, they are independent on the algorithms of geometrical simplification. A prototype is developed and tested using the real world examples. The results show that the approaches in this study are helpful to analyze topological changes for shape simplification.
Keywords: GIS; Topological relations; Shape decomposition; Shape simplification; Topological changes
Shadow elimination and vehicles classification approaches in traffic video surveillance context BIBAKFull-Text 333-345
  H. Asaidi; A. Aarab; M. Bellouki
Video surveillance on highway is a hot topic and a great challenge in Intelligent Transportation Systems. In such applications requiring objects extraction, cast shadows induce shape distortions and object fusions interfering performance of high level algorithms. Shadow elimination allows to improve the performances of video object extraction, classification and tracking. In other hand, it is very important to recognize the type of a detected object in order to track reliably and estimate traffic parameters correctly. This paper presents two approaches to enhance automatic traffic surveillance systems. The first deals with the elimination of shadows and the second concerns the classification of vehicles, based on robust vision and image processing. For moving shadow elimination, a contrast model is proposed to describe and remove dynamic shadows based on the idea that a shadow transformation is a change in contrast. For vehicles classification, Hu moments are calculated in a manner to reduce the perspective effects and used to describe vehicles in knowledge base. Experimental results on the various challenging video sequences show that the proposed approach outperforms classification methods of related works (with a classification accuracy of 96.96%), and that the shadow elimination approach performs better than compared works (with detection rate of 95-99% and discrimination rate of 85.7-89%).
Keywords: Intelligent Transportation System; Shadow elimination; Video surveillance; Vehicles classification; Traffic parameters estimation
Static type information to improve the IDE features of hybrid dynamically and statically typed languages BIBAKFull-Text 346-362
  Francisco Ortin; Francisco Moreno; Anton Morant
The flexibility offered by dynamically typed programming languages has been appropriately used to develop specific scenarios where dynamic adaptability is an important issue. This has made some existing statically typed languages gradually incorporate more dynamic features to their implementations. As a result, there are some programming languages considered hybrid dynamically and statically typed. However, these languages do not perform static type inference on a dynamically typed code, lacking those common features provided when a statically typed code is used. This lack is also present in the corresponding IDEs that, when a dynamically typed code is used, do not provide the services offered for static typing. We have customized an IDE for a hybrid language that statically infers type information of dynamically typed code. By using this type information, we show how the IDE can provide a set of appealing services that the existing approaches do not support, such as compile-time type error detection, code completion, transition from dynamically to statically typed code (and vice versa), and significant runtime performance optimizations. We have evaluated the programmer's performance improvement obtained with our IDE, and compared it with similar approaches.
Keywords: Hybrid dynamic and static typing; IDE support; Type inference; Code completion; Separation of concerns; Plug-in; Visual Studio
A reactive extension of the OpenMusic visual programming language BIBAKFull-Text 363-375
  Jean Bresson; Jean-Louis Giavitto
Objectives: OpenMusic (OM) is a domain-specific visual programming language designed for computer-aided music composition. This language based on Common Lisp allows composers to develop functional processes generating or transforming musical data, and to execute them locally by demand-driven evaluations. As most historical computer-aided composition environments, OM relies on a transformational declarative paradigm, which is hard to conciliate with reactive data-flow (an evaluation scheme more adequate to the development of interactive systems). We propose to link these two evaluation paradigms in the same and consistent visual programming framework.
   Methods: We establish a denotational semantics of the visual language, which gives account for its demand-driven evaluation mechanism and the incremental construction of programs. We then extend this semantics to enable reactive computations in the functional graphs.
   Results: The resulting language merges data-driven executions with the existing demand-driven mechanism. A conservative implementation is proposed.
   Conclusions: We show that the incremental construction of programs and their data-driven and demand-driven evaluations can be smoothly integrated in the visual programming workflow. This integration allows for the propagation of changes in the programs, and the evaluation of graphically designed functional expressions as a response to external events, a first step in bridging the gap between computer-assisted composition environments and real-time musical systems.
Keywords: Visual programming; Functional languages; Reactive data flow; Propagation; Evaluation strategy; Computer-aided composition
Hierarchical crowd analysis and anomaly detection BIBAKFull-Text 376-393
  Xinyi Chong; Weibin Liu; Pengfei Huang; Norman I. Badler
Objective: This work proposes a novel approach to model the spatiotemporal distribution of crowd motions and detect anomalous events.
   Methods: We first learn the regions of interest (ROIs) which inform the behavioral patterns by trajectory analysis with Hierarchical Dirichlet Processes (HDP), so that the main trends of crowd motions can be modeled. Based on the ROIs, we then build a series of histograms both on global and local levels as the templates for the observed movement distribution, which statistically describes time-correlated crowd events. Once the template has been built hierarchically, we import real data containing the discrete trajectory observations from video surveillance and detect abnormal events for individuals and for crowds.
   Results: Experimental results show the effectiveness of our approach, which is able to analyze and extract the crowd motion information from observed trajectory dataset, and achieve the anomaly detection at the hierarchical levels.
   Conclusion: The proposed hierarchical approach can learn the moving trends of crowd both in global and local area and describe the crowd behaviors in statistical way, which build a template for pedestrian movement distribution that allows for the detection of time-correlated abnormal crowd events.
Keywords: Crowd analysis; Anomaly detection; Video surveillance; Hierarchical Dirichlet Process; Trajectory analysis
VIRTUE: A visual tool for information retrieval performance evaluation and failure analysis BIBAKFull-Text 394-413
  Marco Angelini; Nicola Ferro; Giuseppe Santucci; Gianmaria Silvello
Objective: Information Retrieval (IR) is strongly rooted in experimentation where new and better ways to measure and interpret the behavior of a system are key to scientific advancement. This paper presents an innovative visualization environment: Visual Information Retrieval Tool for Upfront Evaluation (VIRTUE), which eases and makes more effective the experimental evaluation process.
   Methods: VIRTUE supports and improves performance analysis and failure analysis. Performance analysis: VIRTUE offers interactive visualizations based on well-known IR metrics allowing us to explore system performances and to easily grasp the main problems of the system.
   Failure analysis: VIRTUE develops visual features and interaction, allowing researchers and developers to easily spot critical regions of a ranking and grasp possible causes of a failure. Results: VIRTUE was validated through a user study involving IR experts. The study reports on (a) the scientific relevance and innovation and (b) the comprehensibility and efficacy of the visualizations.
   Conclusion: VIRTUE eases the interaction with experimental results, supports users in the evaluation process and reduces the user effort. Practice: VIRTUE will be used by IR analysts to analyze and understand experimental results.
   Implications: VIRTUE improves the state-of-the-art in the evaluation practice and integrates visualization and IR research fields in an innovative way.
Keywords: Information retrieval; Experimental evaluation; Visual analytics; Performance analysis; Failure analysis
End-User Development of Mashups with NaturalMash BIBAKFull-Text 414-432
  Saeed Aghaee; Cesare Pautasso
Context: The emergence of the long-tail in the market of software applications is shifting the role of end-users from mere consumers to becoming developers of applications addressing their unique, personal, and transient needs. On the Web, a popular form of such applications is called mashup, built out of the lightweight composition of Web APIs (reusable software components delivered as a service through the Web). To enable end-users to build mashups, there is a key problem that must be overcome: End-users lack programming knowledge as well as the interest to learn how to master the complex set of Web technologies required to develop mashups. End-User Development (EUD) is an emerging research field dealing with this type of problems. Its main goal is to design tools and techniques facilitating the development of software applications by non-programmers.
   Objective: The paper describes the design and evaluation of NaturalMash, an innovative EUD tool for mashups (a mashup tool). NaturalMash aims at enabling non-professional users without any knowledge of programming languages and skills to create feature-rich, interactive, and useful mashups.
   Methods: The design of NaturalMash adopts a formative evaluation approach, and has completed three design and evaluation iterations. The formative evaluations utilize usability testing, think aloud protocol, questionnaires, observation, and unstructured interviews. Additionally, we compare the expressive power of NaturalMash with the state-of-the-art mashup tools.
   Results: The results from the formative evaluations helped us identify important usability problems. From an assessment point of view, the results were promising and suggested that the proposed tool has a short and gentle learning curve in a way that even non-programmers are able to rapidly build useful mashups. Also, the comparative evaluation results showed that NaturalMash offers a competitive level of expressive power compared with existing mashup tools targeting non-programmers.
   Conclusion: As the evaluation results indicate, NaturalMash provides a high level of expressive power while it is still highly usable by non-programmers. These suggest that we have successfully achieved the objective of the proposed tool, distinguishing it from existing mashup tools that are either too limited or highly specialized for non-professional users.
Keywords: Mashups; End-User Development; Mashup tools; WYSIWYG; Natural language programming; Programming by Demonstration
Network visualization for financial crime detection BIBAKFull-Text 433-451
  Walter Didimo; Giuseppe Liotta; Fabrizio Montecchiani
Objective: We present a new software system, VisFAN, for the visual analysis of financial activity networks.
   Methods: We combine enhanced graph drawing techniques to devise novel algorithms and interaction functionalities for the visual exploration of networked data sets, together with tools for SNA and for the automatic generation of reports.
   Results: An application example constructed on real data is presented. We also report the results of a study aimed at qualitatively understanding the satisfaction level of the analysts when using VisFAN.
   Conclusion: VisFAN makes a strong use of visual interactive tools, combined with ad-hoc clustering techniques and customizable layout constraints management.
   Implications: As this system confirms, information visualization can play a crucial role to face the discovery of financial crimes.
Keywords: Financial crime detection; Graph visualization; Social network analysis; Information visualization
Larger crossing angles make graphs easier to read BIBAKFull-Text 452-465
  Weidong Huang; Peter Eades; Seok-Hee Hong
Objective: Aesthetics are important in algorithm design and graph evaluation. This paper presents two user studies that were conducted to investigate the impact of crossing angles on human graph comprehension.
   Method and results: These two studies together demonstrate our newly proposed two-step approach for testing graph aesthetics. The first study is a controlled experiment with purposely-generated graphs. Twenty-two subjects participated in the study and were asked to determine the length of a path which was crossed by a set of parallel edges at different angles. The result of an analysis of variance showed that larger crossing angles induced better task performance. The second study was a non-controlled experiment with general real world graphs. Thirty-seven subjects participated in the study and were asked to find the shortest path of two pre-selected nodes in a set of graph drawings. The results of simple regression tests confirmed the negative effect of small crossing angles. This study also showed that among our four proposed candidates, the minimum crossing angle on the path was the best measure for the aesthetic when path finding is important.
   Conclusion: Larger crossing angles make graphs easier to read.
   Implications: In situations where crossings cannot be completely removed (for example, graphs are non-planar, or a drawing convention is applied), or where effort needed to remove all crossings cannot be justified, the crossing angle should be maximized to reduce the negative impact of crossings to the minimum.
Keywords: Graph drawing; Node-link diagram; Aesthetic; Crossing angle; Edge crossing; Perception; Evaluation
Representing time intervals in a two-dimensional space: An empirical study BIBAKFull-Text 466-480
  Yi Qiang; Martin Valcke; Philippe De Maeyer; Nico Van de Weghe
Objective: Instead of the linear model (LM), time intervals can be represented by a two-dimensional (2D) model, which is called the triangular model (TM). Although the TM has been introduced for decades and applied in some areas, there still a lack of empirical studies on its usability. To fill this gap, this study aims to evaluate how people perform when using the TM to answer questions on time intervals, in comparison with using the traditional LM.
   Method: Around 250 novice participants took part in the experiment, which consisted of a video training, a pretest and posttest. The video training introduced the basic knowledge of temporal relations and the two representations. The pretest allowed participants to practice the knowledge they have learned and receive feedbacks of the answers. In the posttest, participants' accuracy and speed when answering the questions were recorded for analysis. The results of using the TM and the LM were compared in pairs. The null hypothesis is that the participants produce equal results with the two models.
   Result: The results showed that the participants scored better and spent less time when answering questions with the TM, which rejected the null hypothesis. Moreover, the score and speed when they used the TM did decline in the questions containing a larger number of intervals. In contrast, the score and accuracy when they used the LM declined when questions containing a large number of intervals.
  • The TM is easy to learn. After a 20-min training, novice participants can use
       it to solve questions and produce satisfactory result.
  • The TM is easy and efficient for visual queries of time intervals.
  • The TM is easy to use for handling a large number of intervals. Implication:
  • The TM can be widely applied in analysing time intervals and linear data.
  • Tools implementing the TM can be learned and used by novice users.
    Keywords: Temporal reasoning; Time intervals; Information visualisation; Temporal information; Empirical study
  • Pencil-like sketch rendering of 3D scenes using trajectory planning and dynamic tracking BIBAKFull-Text 481-493
      Günay Orbay; Levent Burak Kara
    Objective: We present a new non-photorealistic rendering method to render 3D scenes in the form of pencil-like sketches.
       Methods: This work is based on the observation that the dynamic feedback mechanism involving the human visual system and the motor control of the hand collectively generates the visual characteristics unique to hand-drawn sketches. At the heart of our approach is a trajectory planning and tracking algorithm that generate the sketch in multiple layers using a dynamic pen model. On each layer, a set of target strokes are generated from the silhouette lines, edges, and shaded regions which serve as the target trajectory for a closed-loop dynamic pen model. The pen model then produces the rendered sketch, whose characteristics can be adjusted with a set of trajectory and tracking parameters. This process continues in several layers until the tonal difference between the sketch and the original 3D render is minimized.
       Results: We demonstrate our approach with examples that are created by controlling the parameters of our sketch rendering algorithms.
       Conclusion: The examples not only show typical sketching artifacts that are common to human-drawn sketches but also demonstrate that it is capable of producing multiple sketching styles.
    Keywords: Non-photorealistic rendering; Dynamic pen model; Drawing style
    Distributed modeling of use case diagrams with a method based on think-pair-square: Results from two controlled experiments BIBAKFull-Text 494-517
      Giuseppe Scanniello; Ugo Erra
    Objective: In this paper, we present the results of two controlled experiments conducted to assess a new method based on think-pair-square in the distributed modeling of use case diagrams.
       Methods: This new method has been implemented within an integrated environment, which allows distributed synchronous modeling and communication among team members. To study the effect of the participants' familiarity with the method and the integrated environment, the second experiment is a replication conducted with the same participants as the original experiment. The results show a significant difference in favor of face-to-face (i.e., the chosen baseline) for the time to complete modeling tasks, with no significant impact on the quality of the produced models.
       Results: The results on participants; familiarity indicate a significant effect on the task completion time (i.e., more familiar participants spent less time), with no significant impact on quality.
       Practice: One of the most interesting practical implications of our study is -- in case the time difference is not an issue, but moving people might be a problem, the new method and environment could represent a viable alternative to face-to-face. Another significant result is that also people not perfectly trained on our method and environment may benefit from their use: the training phase could be shortened or skipped. In addition, face-to-face is less prone to consolidate participants' working style and to develop a shared working habit of participants.
       Implications: This work is in the direction of the media-effect theories applied to requirements engineering. The results indicate that the participants in the experiments significantly spent less time when modeling use case diagrams using face-to-face. Conversely, no significant difference was observed on the quality of the artifacts produced by the participants in the these tasks.
    Keywords: Experiments; Distributed Software Development; Requirements Modeling
    Set space diagrams BIBAKFull-Text 518-532
      Björn Gottfried
    This paper introduces set space diagrams and defines their formal syntax and semantics. Conventional region based diagrams, like Euler circles and Venn diagrams, represent sets and their intersections by means of overlapping regions. By contrast, set space diagrams provide a certain layout that avoids overlapping geometrical entities. This enables the representation of a good deal of sets without getting diagrams which are cluttered due to overlapping regions. In particular, these diagrams can be employed for illustration purposes, e.g., for showing the laws of Boolean algebras. Additionally, cardinalities are represented and can be easily compared; inferences can be drawn to derive unknown cardinalities from a given knowledge base. The soundness of set space diagrams is shown with respect to their set-theoretic interpretation.
    Keywords: Diagrammatic reasoning; Set theory; Set space diagrams; Boolean algebra; Cardinalities; Euler circles; Venn diagrams
    Techniques for Edge Stratification of Complex Graph Drawings BIBAKFull-Text 533-543
      Emilio Di Giacomo; Walter Didimo; Giuseppe Liotta; Fabrizio Montecchiani; Ioannis G. Tollis
    We propose an approach that allows a user (e.g., an analyst) to explore a layout produced by any graph drawing algorithm, in order to reduce the visual complexity and clarify its presentation. Our approach is based on stratifying the drawing into layers with desired properties; to this aim, heuristics are presented. The produced layers can be explored and combined by the user to gradually acquire details. We present a user study to test the effectiveness of our approach. Furthermore, we performed an experimental analysis on popular force-directed graph drawing algorithms, in order to evaluate what is the algorithm that produces the smallest number of layers and if there is any correlation between the number of crossings and the number of layers of a graph layout. The proposed approach is useful to explore graph layouts, as confirmed by the presented user study. Furthermore, interesting considerations arise from the experimental evaluation, in particular, our results suggest that the number of layers of a graph layout may represent a reliable measure of its visual complexity. The algorithms presented in this paper can be effectively applied to graph layouts with a few hundreds of edges and vertices. For larger drawings that contain lots of crossings, the time complexity of our algorithms grows quadratically in the number of edges and more efficient techniques need to be devised. The proposed approach takes as input a layout produced by any graph drawing algorithm, therefore it can be applied in a variety of application domains. Several research directions can be explored to extend our framework and to devise new visualization paradigms to effectively present stratified drawings.
    Keywords: Network exploration; Human-computer interaction; Graph visualization; Information visualization

    VLC 2014-10 Volume 25 Issue 5

    Palimpsest: A layered language for exploratory image processing BIBAKFull-Text 545-571
      Alan F. Blackwell
    Palimpsest is a novel purely-visual language intended to support exploratory live programming. It demonstrates a new paradigm for the visual representation of constraint programming that may be appropriate to future generations of keyboardless and touchscreen devices. The current application domain is that of creative image manipulation, although the paradigm can support a wider range of computational expression. The combination of constraint semantics expressed via a novel image-layering metaphor provides a new approach to supporting a gradual slope of abstraction from direct manipulation to behaviour specification. Exploratory evaluations with a range of users give an indication of likely audiences, and opportunities for future development and application.
    Keywords: Visual programming; Visual arts; Live coding; Constraint semantics
    Gestures that people can understand and use BIBAKFull-Text 572-576
      Carmelo Ardito; Maria Francesca Costabile; Hans-Christian Jetter
    Recent advances in computing devices push researchers to envision new interaction modalities that go beyond traditional mouse and keyboard input. Typical examples are large displays for which researchers hope to create more "natural" means of interaction by using human gestures and body movements as input. In this article, we reflect about this goal of designing gestures that people can easily understand and use and how designers of gestural interaction can capitalize on the experience of 30 years of research on visual languages to achieve it. Concretely, we argue that gestures can be regarded as "visual expressions to convey meaning" and thus are a visual language. Based on what we have learned from visual language research in the past, we then explain why the design of a generic gesture set or language that spans many applications and devices is likely to fail. We also discuss why we recommend using gestural manipulations that enable users to directly manipulate on-screen objects instead of issuing commands with symbolic gestures whose meaning varies among different users, contexts, and cultures.
    Keywords: Gestural languages; Visual expressions; Symbolic gestures; Manipulations
    Design, realization and user evaluation of the SmartVortex Visual Query System for accessing data streams in industrial engineering applications BIBAKFull-Text 577-601
      Emanuela Bauleo; Serena Carnevale; Tiziana Catarci; Stephen Kimani; Mariano Leva; Massimo Mecella
    Objective: In this paper we present a Visual Query System, which allows users to graphically build queries over data streams and traditional relational data. The Visual Query System runs on top of a DSMS (Data Stream Management System).
       Methods: The system has been designed and implemented following the user-centered design approach. Two different releases of the system have been incrementally and iteratively designed and evaluated. The first release has been evaluated using heuristic evaluation. The second release, whose design was a refinement based on the results of the foregoing heuristic evaluation, was evaluated by several users. Moreover, a comparative evaluation involving users has been conducted on the second release.
       Results: The paper presents the visual query system, and the results of the various evaluations.
       Conclusion: Visual Query Systems for data streams are an effective tool for industrial engineers in querying and analyzing data streams from equipments.
       Practice and implications: The proposed visual query system has been employed in real industrial scenarios in order to visually query and analyze data streams produced by industrial machines.
    Keywords: Visual Query System (VQS); Data Stream Management System (DSMS); Industrial engineering; Usability evaluation
    A language for representing and extracting 3D geometry semantics from paper-based sketches BIBAKFull-Text 602-624
      Philip Farrugia; Kenneth P. Camilleri; Jonathan C. Borg
    Every product that exists, ranging from a toothbrush to a car, has first been conceived as a mental concept. Due to its efficacy in rapidly externalizing concepts, paper-based sketching is still extensively used by practising designers to gradually develop the three-dimensional (3D) geometric form of a concept. It is a common practice that form concepts are sketched on paper prior to generating 3D virtual models in commercial Computer-Aided Design (CAD) systems. However, the user-interface of such systems does not support automatic generation of 3D models from sketches. Furthermore, the inherent characteristics of form sketching (e.g. idiosyncrasy) pose a challenge to computer-based understanding of the form concept semantics expressed on paper. To address these issues, this paper is therefore concerned with the development of a visual language that is prescribed and to be used by product designers to annotate paper-based sketches such that the form geometry semantics can be formally represented; parsing the annotated sketch allows for the automatic generation of 3D virtual models in CAD. Inspired by re-usable 3D CAD modelling functions and the related environmental constraints and requirements, a prescribed sketching language, PSL, has been developed to annotate paper-based form sketches. The framework architecture which parses the annotated sketch and subsequently extracts the form concept semantics is described. Based on this framework, a prototype computer tool has been implemented and evaluated. Evaluation results provide a degree of evidence, first on the suitability of PSL in representing the semantics of a range of forms, and secondly on the designers' acceptance of taking up this annotated sketching approach in practice.
    Keywords: Human-computer interaction; Computer-aided sketching; 3D modelling
    Erratum to "A Reactive Extension of the OpenMusic Visual Programming Language" Journal of Visual Languages and Computing (2014) pp. 363-375. BIBFull-Text 625
      Jean Bresson; Jean-Louis Giavitto