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Journal of Visual Languages & Computing 22

Editors:S.-K. Chang; Stefano Levialdi
Standard No:ISSN: 1045-926X
Links:Table of Contents
  1. VLC 2011-02 Volume 22 Issue 1
  2. VLC 2011-04 Volume 22 Issue 2
  3. VLC 2011-06 Volume 22 Issue 3
  4. VLC 2011-08 Volume 22 Issue 4
  5. VLC 2011-10 Volume 22 Issue 5
  6. VLC 2011-12 Volume 22 Issue 6

VLC 2011-02 Volume 22 Issue 1

Special Issue on Visual Languages and Logic: Guest editors' introduction BIBFull-Text 1-2
  Philip Cox; Andrew Fish; John Howse
VMQL: A visual language for ad-hoc model querying BIBAKFull-Text 3-29
  Harald Störrle
In large scale model based development, analysis level models are more like knowledge bases than engineering artifacts. Their effectiveness depends, to a large degree, on the ability of domain experts to retrieve information from them ad-hoc. For large scale models, however, existing query facilities are inadequate.
   The visual model query language (VMQL) is a novel approach that uses the respective modeling language of the source model as the query language, too. The semantics of VMQL is defined formally based on graphs, so that query execution can be defined as graph matching. VMQL has been applied to several visual modeling languages, implemented, and validated in small case studies, and several controlled experiments.
Keywords: Model querying; Unified modeling language (UML); Object constraint language (OCL); Domain specific languages (DSL); End user modelers
Visually specifying compliance rules and explaining their violations for business processes BIBAKFull-Text 30-55
  Ahmed Awad; Matthias Weidlich; Mathias Weske
A business process is a set of steps designed to be executed in a certain order to achieve a business value. Such processes are often driven by and documented using process models. Nowadays, process models are also applied to drive process execution. Thus, correctness of business process models is a must. Much of the work has been devoted to check general, domain-independent correctness criteria, such as soundness. However, business processes must also adhere to and show compliance with various regulations and constraints, the so-called compliance requirements. These are domain-dependent requirements.
   In many situations, verifying compliance on a model level is of great value, since violations can be resolved in an early stage prior to execution. However, this calls for using formal verification techniques, e.g., model checking, that are too complex for business experts to apply. In this paper, we utilize a visual language, BPMN-Q, to express compliance requirements visually in a way similar to that used by business experts to build process models. Still, using a pattern based approach, each BPMN-Q graph has a formal temporal logic expression in computational tree logic (CTL). Moreover, the user is able to express constraints, i.e., compliance rules, regarding control flow and data flow aspects. In order to provide valuable feedback to a user in case of violations, we depend on temporal logic querying approaches as well as BPMN-Q to visually highlight paths in a process model whose execution causes violations.
Keywords: Business process modeling; Compliance checking; Visual modeling; Anti-patterns
Reasoning with coincidence grids -- A sequent-based logic and an analysis of complexity BIBAKFull-Text 56-65
  Dave Barker-Plummer; Nik Swoboda
Information is often represented in tabular format in everyday documents such as balance sheets, sales figures, and so on. Tables represent an interesting point in the spectrum of representation systems between pictures and sentences, since some aspects of tables are sentential or conventional in nature, while others are graphical. In this paper we describe a sequent-based logic for a particular formalized tabular representation system, that of coincidence grids. After presenting this system we will then provide an analysis of the complexity of reasoning with this formalism showing that the problem of deciding whether a coincidence grid can be consistently completed is NP-Complete.
Keywords: Coincidence grid; Logic grid puzzle; Logic matrix puzzle; Diagrammatic reasoning
Constructing a bidirectional transformation between BPMN and BPEL with a functional logic programming language BIBAKFull-Text 66-89
  Steffen Mazanek; Michael Hanus
In this article we show how functional logic programming techniques can be used to construct a bidirectional transformation between structured process models of the business process modeling notation (BPMN) and executable models of the business process execution language (BPEL). We specify the abstract syntax of structured process models by a context-free hypergraph grammar. This grammar can be subsequently transformed into a graph parser using our previously developed Grappa framework of functional logic GRAPh PArser combinators. The Grappa framework has been implemented using the functional logic programming language Curry. Furthermore, we show how the constructed parsers can be enriched with semantic computations as required for the synthesis of BPEL from BPMN. Since our parser is a function implemented in a functional logic language, it can be applied in both directions. Thus, given a BPEL model, a corresponding BPMN graph can be constructed with the very same parser. Finally, logic-based parsers can be used for model completion and language generation in a straightforward way.
   In order to be self-contained, this article also surveys context-free hypergraph grammars, the concepts of the programming language Curry, the example languages BPMN and BPEL, and the ideas of the Grappa framework. Actually, this article is a literate Curry program and, as such, directly executable. Thus, it contains the complete concise source code of our application.
Keywords: Graph parsing; Functional logic programming; Parser combinators; Curry; Business process models; BPMN; BPEL
A decision procedure for a decidable fragment of generalized constraint diagrams BIBAKFull-Text 90-105
  Jim Burton; Gem Stapleton; Ali Hamie
Constraint diagrams were introduced by Kent, in 1997, as an alternative to the OCL for placing formal constraints on software models. Since their introduction, constraint diagrams have evolved and, after a careful analysis of their positive and negative features, generalized constraint diagrams were proposed. An important benefit of providing a formal model of a software system (diagrammatically or otherwise) is the ability to determine whether that model is consistent (i.e. satisfiable). However, determining satisfiability in an algorithmic, terminating, way is only possible in decidable logics. In this paper, we consider the so-called unitary existential fragment (UEF) of generalized constraint diagrams and, within this fragment, identify a decision procedure for the satisfiability of a particular class of diagrams. We then demonstrate how to extend the decision procedure to the UEF as a whole. This work lays the foundations for providing decision procedures for larger fragments of generalized constraint diagrams and we discuss how this might be achieved in the paper.
Keywords: Constraint diagrams; Consistency; Visual logic; Formal diagrammatic reasoning

VLC 2011-04 Volume 22 Issue 2

Generating sample looks for geometric objects in a visual design language BIBAKFull-Text 107-119
  Omid Banyasad; Philip T. Cox
A major application of visualisation is to the design of structured objects such as buildings, machinery and electronic circuits, as in computer-aided design (CAD) systems. Complex designs are frequently parameterised so that they represent families of objects rather than single artifacts, and building them requires design environments that support both the concrete visualisation and manipulation of components, and the abstract specification of how they are related. CAD systems usually separate these two aspects, providing the abstract programming capability via a textual programming language grafted on to a 3D object editor and solid modeller.
   A recently proposed design language merges these two activities by embedding representations of solid objects in a visual logic programming language. A practical issue that arises is how to automatically generate a "sample look", a reasonable representation for a parameterised object which can be displayed during execution (assembly) of a design. We present a solution to this problem based on "factoring", which separates the constraints on a solid object from its geometric properties.
Keywords: Design language; Logic programming; Computer-aided design; Solid modelling; Sample look; Design space
Navigating within news collections using tag-flakes BIBAKFull-Text 120-139
  Luigi Di Caro; K. Selçuk Candan; Maria Luisa Sapino
The use of tag clouds is common for presenting frequently occurring tags or keywords in a collection to the users. Most visualizations of tag clouds vary the sizes of the fonts to differentiate important tags from others. This, however, is sufficient neither to help the user explore and discover relationships between tags in a collection, nor to help track the changes in these relationships across time frames in dynamic collections. In this paper, we propose an alternative "contextual-layout" method, tag-flakes, for presenting tags or keywords that are associated with dynamically evolving textual content, like news streams. A TMine algorithm first maps tags onto a latent semantic space. However, instead of using this latent semantic space to simply cluster and index the documents (as commonly done in many existing schemes), TMine analyzes the relationships between tags in this semantic space and the resulting tag cloud is condensed into a hierarchy (or a tag-flake) in a way that captures contextual relationships between tags: descendant terms in the hierarchy occur within the context defined by the ancestor terms. This provides a mechanism for navigation within the tag space as well as for the contextual organization of the text documents. We use TMine in developing the tagFlake visualization system, which relies on TMine for organizing tags extracted from news collections in a hierarchical manner and supports navigation within the collection through these contextually laid-out tag clouds. tagFlake also helps users track topic developments and changes in the context in which certain keywords are used. Experimental evaluation results show the effectiveness of the proposed TMine method in capturing the semantic structures of collections.
Keywords: Tag clouds; Tag hierarchies; Visualization and navigation through news collections; Tracking
Developing usable web interfaces with the aid of automatic verification of their formal specification BIBAKFull-Text 140-149
  Rosanna Cassino; Maurizio Tucci
The development of interactive visual applications is a complex work, usually performed with the help of advanced visual programming environments. Although a number of tools are available to support designers and developers in the specification of a GUI's layout and behavior, and in the generation of the corresponding code that implements the interface, theoretical guidelines and/or semi-automatic mechanisms rely upon the knowledge of the designer to manage usability and accessibility issues. Indeed, the evaluation of the visual environments is traditionally performed by means of expert-based evaluations or by testing with end users. In this work we describe a methodology to specify and evaluate interactive visual environments, in particular web interfaces, based on the SR-Action Grammars formalism and we present a bottom-up approach to aid the designer to develop graphical applications that automatically respect a significant number of usability rules before the software is released and tested by standard methods. We show how it is possible to assess the usability metrics of consistency, completeness and user control by means of checks performed at a high level of abstraction. VALUTA (Automatic Tool for the Usability Verification at Abstract Level) is the implemented tool that allows developers to generate the formal specification of an interactive visual application in automatic manner, so to perform the related usability controls at a very early stage. Thanks to usability controls automatically performed at formal level, the designer can use the evaluation results to perform feedback analysis of the visual environment. The tool is applicable to an already existing interface, allowing the designer to evaluate its usability in the development of a more usable version. We have analyzed the home page of three web sites (www.lycos.it, www.google.it, http://it.mail.yahoo.com/) as a case study and we show the related evaluation report generated by the described approach.
Keywords: Graphical user interface; Usability evalution; Grammars formalism
eStorys: A visual storyboard system supporting back-channel communication for emergencies BIBAKFull-Text 150-169
  A. Malizia; A. Bellucci; P. Diaz; I. Aedo; S. Levialdi
In this paper we present a new web mashup system for helping people and professionals to retrieve information about emergencies and disasters. Today, the use of the web during emergencies, is confirmed by the employment of systems like Flickr, Twitter or Facebook as demonstrated in the cases of Hurricane Katrina, the July 7, 2005 London bombings, and the April 16, 2007 shootings at Virginia Polytechnic University. Many pieces of information are currently available on the web that can be useful for emergency purposes and range from messages on forums and blogs to georeferenced photos. We present here a system that, by mixing information available on the web, is able to help both people and emergency professionals in rapidly obtaining data on emergency situations by using multiple web channels. In this paper we introduce a visual system, providing a combination of tools that demonstrated to be effective in such emergency situations, such as spatio/temporal search features, recommendation and filtering tools, and storyboards. We demonstrated the efficacy of our system by means of an analytic evaluation (comparing it with others available on the web), an usability evaluation made by expert users (students adequately trained) and an experimental evaluation with 34 participants.
Keywords: Mashups; Collaboration systems; Emergency management

VLC 2011-06 Volume 22 Issue 3

Special issue on visual analytics and visual semantics: Guest Editors' introduction BIBFull-Text 171-172
  Gem Stapleton; Giuliana Vitiello; Monica Sebillo
A chorem-based approach for visually analyzing spatial data BIBAKFull-Text 173-193
  Davide De Chiara; Vincenzo Del Fatto; Robert Laurini; Monica Sebillo; Giuliana Vitiello
The need to support the activities of decision makers through highly interactive visual environments has motivated the growing interest in the area of GeoVisual Analytics. New interactive visualization tools are being envisaged to deal with large datasets in order to synthesize information and perform complex analytical tasks. Along this line, our research efforts have been focusing on new cartographic approaches which could support daily analysts' work by producing synthesis and presentation of discovered patterns in a concise and understandable way. As a result, we have proposed the adoption of chorems as an innovative method to visually summarize information from spatial databases and we have implemented an XML-based language, named ChorML, able to both specify chorems characterizing a map and store the information useful to their manipulation.
   The goal of the present paper is to enhance the role that chorems may play in geographic domains, by exploiting them also for querying and accessing data associated with a phenomenon under investigation. To develop this idea, we first extend the semantics associated with the chorem concept and define a set of operators useful for the rapid analysis of spatio-temporal phenomena. Then, starting from an initial prototype, we present a chorem-based visual environment that integrates traditional interactive visualization and analysis techniques. The environment is specifically conceived so that each visual interaction task has a context-sensitive behavior, which allows users to acquire specific information from the underlying spatial database. Finally, we present an enhanced version of ChorML language, able to support the new analysis functionalities on chorems.
Keywords: Visual Analytics; Geovisualization; Spatial Data; Geographic Patterns; Human Computer Interaction Advanced Cartographic Solutions
Improving visual analytics environments through a methodological framework for automatic clutter reduction BIBAKFull-Text 194-212
  Enrico Bertini; Giuseppe Santucci
One of the main visual analytics characteristics is the tight integration between automatic computations and interactive visualization. This generally corresponds to the availability of powerful algorithms that allow for manipulating the data under analysis, transforming it in order to feed suitable visualizations.
   This paper focuses on more general purpose automatic computations and presents a methodological framework that can improve the quality of the visualizations adopted in the analytical process, using the dataset at hand and the actual visualization.
   In particular, the paper deals with the critical issue of visual clutter reduction, presenting a general strategy for analyzing and reducing it through random data sampling. The basic idea is to model the visualization in a virtual space in order to analyze both clutter and data features (e.g., absolute density, relative density, etc.). In this way we can measure the visual overlapping which may likely affects a visualization while representing a large dataset, obtaining precise visual quality metrics about the visualization degradation and devising automatic sampling strategies in order to improve the overall image quality. Metrics and algorithms have been tuned taking into account the results of suitable user studies. We will describe our proposal using two running case studies, one on 2D scatterplots and the other one on parallel coordinates.
Keywords: Visual analytics; Information visualization; Scatterplot; Parallel coordinates; Visual quality metrics; Clutter reduction
A conceptual framework and taxonomy of techniques for analyzing movement BIBAKFull-Text 213-232
  G. Andrienko; N. Andrienko; P. Bak; D. Keim; S. Kisilevich; S. Wrobel
Movement data link together space, time, and objects positioned in space and time. They hold valuable and multifaceted information about moving objects, properties of space and time as well as events and processes occurring in space and time. We present a conceptual framework that describes in a systematic and comprehensive way the possible types of information that can be extracted from movement data and on this basis defines the respective types of analytical tasks. Tasks are distinguished according to the type of information they target and according to the level of analysis, which may be elementary (i.e. addressing specific elements of a set) or synoptic (i.e. addressing a set or subsets). We also present a taxonomy of generic analytic techniques, in which the types of tasks are linked to the corresponding classes of techniques that can support fulfilling them. We include techniques from several research fields: visualization and visual analytics, geographic information science, database technology, and data mining.
   We expect the taxonomy to be valuable for analysts and researchers. Analysts will receive guidance in choosing suitable analytic techniques for their data and tasks. Researchers will learn what approaches exist in different fields and compare or relate them to the approaches they are going to undertake.
Keywords: Moving object; Trajectory; Movement data; Visual analytics
Using rule overriding to improve reusability and understandability of Dynamic Meta Modeling specifications BIBAKFull-Text 233-250
  Christian Soltenborn; Gregor Engels
Dynamic Meta Modeling (DMM) is a visual semantics specification technique targeted at languages based on a metamodel. A DMM specification consists of a runtime metamodel and operational rules which describe how instances of the runtime metamodel change over time. A known deficiency of the DMM approach is that it does not support the refinement of a DMM specification, e.g., in the case of defining the semantics for a refined and extended domain-specific language (DSL). Up to now, DMM specifications could only be reused by adding or removing DMM rules.
   In this paper, we enhance DMM such that DMM rules can override other DMM rules, similar to a method being overridden in a subclass, and we show how rule overriding can be realized with the graph transformation tool GROOVE. We argue that rule overriding does not only have positive impact on reusability, but also improves the intuitive understandability of DMM semantics specifications.
Keywords: Semantics; Metamodel; Dynamic Meta Modeling; Graph transformation; Inheritance

VLC 2011-08 Volume 22 Issue 4

Challenging problems of geospatial visual analytics BIBFull-Text 251-256
  Gennady Andrienko; Natalia Andrienko; Daniel Keim; Alan M. MacEachren; Stefan Wrobel
Analytical, visual and interactive concepts for geo-visual analytics BIBAKFull-Text 257-267
  Heidrun Schumann; Christian Tominski
Supporting the visual analysis of structured multivariate geo-spatial data is a challenging task involving many different aspects. In this paper, we describe a systematic view of this task based on Chi's data state reference model. The analytical, visual and interaction components of the systematic view will be instantiated with specific examples that demonstrate how their tight interconnection facilitates exploration and analysis of geo-spatial data. In particular, we address the visualization of hierarchical structures on maps applying an extended focus+context concept. Moreover, we introduce an approach to extracting association rules from geo-spatial data and visualizing them on maps.
Keywords: Visual analytics; Geo-spatial data; Hierarchical data; Extended focus+context; Association analysis
A pandemic influenza modeling and visualization tool BIBAKFull-Text 268-278
  Ross Maciejewski; Philip Livengood; Stephen Rudolph; Timothy F. Collins; David S. Ebert; Robert T. Brigantic; Courtney D. Corley; George A. Muller; Stephen W. Sanders
The National Strategy for Pandemic Influenza outlines a plan for community response to a potential pandemic. In this outline, state and local communities are charged with enhancing their preparedness. In order to help public health officials better understand these charges, we have developed a visual analytics toolkit (PanViz) for analyzing the effect of decision measures implemented during a simulated pandemic influenza scenario. Spread vectors based on the point of origin and distance traveled over time are calculated and the factors of age distribution and population density are taken into effect. Healthcare officials are able to explore the effects of the pandemic on the population through a geographical spatiotemporal view, moving forward and backward through time and inserting decision points at various days to determine the impact. Linked statistical displays are also shown, providing county level summaries of data in terms of the number of sick, hospitalized and dead as a result of the outbreak. Currently, this tool has been deployed in Indiana State Department of Health planning and preparedness exercises, and as an educational tool for demonstrating the impact of social distancing strategies during the recent H1N1 (swine flu) outbreak.
Keywords: Pandemic influenza; Visual analytics; Risk assessment; Geovisualization
iRedistrict: Geovisual analytics for redistricting optimization BIBAKFull-Text 279-289
  Diansheng Guo; Hai Jin
Redistricting is a complex and challenging spatial optimization problem. It is to group a set of spatial objects (such as counties) into a given number of geographically contiguous districts while satisfying multiple criteria and constraints such as equal population, compact shape, and more. The various criteria are often difficult to optimize and the number of potential solutions is very large. Moreover, many criteria are vaguely defined and may not be measured exactly. Therefore, human judgment and domain knowledge are indispensable and critical in the optimization process. In this paper, we present an interactive and computing-assisted approach to redistricting optimization. Our approach leverages the power of user's domain knowledge, judgment, and interactive exploration to (1) flexibly define various criteria/constraints, (2) visually and interactively examine alternative plans and achieve a balance among different criteria, and (3) efficiently and iteratively construct a collection of high-quality plans that are difficult to obtain with existing methods. A computational optimization algorithm is integrated to assist optimization under user-provided criteria and constraints. With the visual analytics approach, a user can quickly derive high-quality redistricting plans that satisfy both individual preferences and mandatory requirements. We demonstrate the capability of the approach and system with two case studies, Iowa congressional redistricting and South Carolina congressional redistricting.
Keywords: Redistricting; Combinatory optimization; Geovisual analytics; Tabu search
An alternative map of the United States based on an n-dimensional model of geographic space BIBAKFull-Text 290-304
  André Skupin; Aude Esperbé
Geographic features have traditionally been visualized with fairly high amount of geometric detail, while relationships among these features in attribute space have been represented at a much coarser resolution. This limits our ability to understand complex high-dimensional relationships and structures existing in attribute space. In this paper, we present an alternative approach aimed at creating a high-resolution representation of geographic features with the help of a self-organizing map (SOM) consisting of a large number of neurons. In a proof-of-concept implementation, we spatialize 200,000+ U.S. Census block groups using a SOM consisting of 250,000 neurons. The geographic attributes considered in this study reflect a more holistic representation of geographic reality than in previous studies. The study includes 69 attributes regarding population statistics, land use/land cover, climate, geology, topography, and soils. This diversity of attributes is informed by our desire to build a comprehensive two-dimensional base map of n-dimensional geographic space. The paper discusses how standard GIS methods and neural network processing are combined towards the creation of an alternative map of the United States.
Keywords: Geographic data; High-dimensional data; Dimensionality reduction; Self-organizing maps
Geovisual evaluation of public participation in decision making: The grapevine BIBAKFull-Text 305-321
  Robert Aguirre; Timothy Nyerges
This article reports on a three-dimensional (time-space) geovisual analytic called a "grapevine." People often use metaphors to describe the temporal and spatial structure of online discussions, e.g., "threads" growing as a result of message exchanges. We created a visualization to evaluate the temporal and spatial structure of online message exchanges based on the shape of a grapevine naturally cultivated in a vineyard. Our grapevine visualization extends up through time with features like buds, nodes, tendrils, and leaves produced as a result of message posting, replying, and voting. Using a rotatable and fully interactive three-dimensional GIS (Geographic Information System) environment, a geovisual analyst can evaluate the quality of deliberation in the grapevine visualization by looking for productive patterns in fine-grained human-computer-human interaction (HCHI) data and then sub-sampling the productive parts for content analysis. We present an example of how we used the technique in a study of participatory interactions during an online field experiment about improving transportation in the central Puget Sound region of Washington called the Let's Improve Transportation (LIT) Challenge. We conclude with insights about how our grapevine could be applied as a general purpose technique for evaluation of any participatory learning, thinking, or decision making situation.
Keywords: Grapevine; Geovisual analytics; Public participation; Decision making; Spatio-temporal events; Human-computer-human interaction

VLC 2011-10 Volume 22 Issue 5

Formal classification of integrity constraints in spatiotemporal database applications BIBAKFull-Text 323-339
  Mehrdad Salehi; Yvan Bédard; Mir Abolfazl Mostafavi; Jean Brodeur
Imposing integrity constraints is an efficient way to improve data quality in databases. Effective imposition of integrity constraints requires their precise distinction and specification. Despite a few efforts for enhancing the distinction and specification of the integrity constraints in spatial and spatiotemporal databases by their classifications, these classifications fail to precisely distinguish between inherently dissimilar integrity constraints. Furthermore, the existing classifications provide imprecise definitions for the classes of integrity constraints. Such shortcomings explain why still diverse terms are used to refer to a same spatial integrity constraint. In this paper, we propose a formal and more exhaustive classification of the integrity constraints in spatiotemporal databases relying on their nature with respect to space, time, and themes. Moreover, a terminology for the integrity constraints of spatiotemporal databases is presented. Finally, we discuss the advantages of the proposed classification in the specification of integrity constraints.
Keywords: Conceptual model; Integrity constraint; Spatiotemporal modeling; Data quality; Spatiotemporal database
User-comprehension of Euler diagrams BIBAKFull-Text 340-354
  Andrew Fish; Babak Khazaei; Chris Roast
Euler diagrams are a diagrammatic system for representing and reasoning with set theoretic statements. Syntactic constraints called wellformedness conditions (WFCs) are often imposed with the intention of reducing comprehension errors, but there is little supporting empirical evidence that they have the desired effect. We report on experiments which support the theory that the WFCs are generally beneficial for novice user comprehension, but we discover that violating some individual WFCs, such as concurrency, can be beneficial. Furthermore, we examine a prioritisation of the WFCs, derived from the user comprehension results, which could be used to prioritise theoretical work on generation problems or to assist in the provision of a choice of a diagram to display to users, for instance. We have used similar materials to our previous 'preference study' for cross comparison purposes. This accumulation of work has motivated the development of a model of the user comprehension with the aim of more closely linking theoretical and empirical works examining effective notation design, general approaches to displaying notations and interacting with notations.
Keywords: Usability of diagrams and mathematical notation; Comprehension of diagrams; Empirical study; Wellformed and non-wellformed Euler diagrams
The Pattern Instance Notation: A simple hierarchical visual notation for the dynamic visualization and comprehension of software patterns BIBAKFull-Text 355-374
  Jason McC. Smith
Design patterns are a common tool for developers and architects to understand and reason about a software system. Visualization techniques for patterns tend to be either highly theoretical in nature or based on a structural view of a system's implementation. The Pattern Instance Notation is a simple notation technique for visualizing design patterns and other abstractions of software engineering. While based on a formal representation of design patterns, PIN is a tool for comprehension or reasoning which requires no formal training or study, and it is suitable for the programmer or designer without a theoretical background. PIN is hierarchical in nature and compactly encapsulates abstractions that may be spread widely across a system in a concise graphical format, while allowing for repeated unveiling of deeper layers of complexity and interaction on demand. It is designed to be used in either a dynamic visualization tool, or as a static representation for documentation and as a teaching aid.
Keywords: Design patterns; Visualization; Education; Comprehension
A decade of research and development on program animation: The Jeliot experience BIBAKFull-Text 375-384
  Mordechai Ben-Ari; Roman Bednarik; Ronit Ben-Bassat Levy; Gil Ebel; Andrés Moreno; Niko Myller; Erkki Sutinen
Jeliot is a program animation system for teaching and learning elementary programming that has been developed over the past decade, building on the Eliot animation system developed several years before. Extensive pedagogical research has been done on various aspects of the use of Jeliot including improvements in learning, effects on attention, and acceptance by teachers. This paper surveys this research and development, and summarizes the experience and the lessons learned.
Keywords: Program animation; Program visualization; Software visualization; Jeliot; Attention; Eye tracking; Conflictive animation; Phenomenography
Visual suggestions for improvements in business process diagrams BIBAKFull-Text 385-399
  Ralf Laue; Ahmed Awad
Business processes are commonly modeled using a graphical modeling language. The most widespread notation for this purpose is business process diagrams in the Business Process Modeling Notation (BPMN). In this article, we use the visual query language BPMN-Q for expressing patterns that are related to possible problems in such business process diagrams. We discuss two classes of problems that can be found frequently in real-world models: sequence flow errors and model fragments that can make the model difficult to understand.
   By using a query processor, a business process modeler is able to identify possible errors in business process diagrams. Moreover, the erroneous parts of the business process diagram can be highlighted when an instance of an error pattern is found. This way, the modeler gets an easy-to-understand feedback in the visual modeling language he or she is familiar with. This is an advantage over current validation methods, which usually lack this kind of intuitive feedback.
Keywords: Business process model; Business process diagram; BPMN-Q; Visualization

VLC 2011-12 Volume 22 Issue 6

A novel three-tiered visualization approach for firewall rule validation BIBAKFull-Text 401-414
  Chi-Shih Chao; Stephen Jen-Hwa Yang
Firewall is one of the most critical elements of the current Internet, which can protect the entire network against attacks and threats. While configuring the firewalls, rule configuration has to conform to, or say be consistent with, the demands of the network security policies such that the network security would not be flawed. For the security consistency, firewall rule editing, ordering, and distribution must be done very carefully on each of the cooperative firewalls, especially in a large-scale and multifirewall-equipped network. Nevertheless, a network operator is prone to incorrectly configure the firewalls because there are typically thousands or hundreds of filtering/admission rules (i.e., rules in the Access Control List file, or ACL for short), which could be set up in a firewall; not mentioning these rules among firewalls affect mutually and can make the matter worse. Under this situation, the network operator would hardly know his/her misconfiguration until the network functions beyond the expectation. For this reason, our work is to build a visualized validation system for facilitating the check of security consistency between the rule configuration of firewalls and the demands of network security policies. To do so, the developed validation system utilizes a three-tiered visualization hierarchy along with different compound viewpoints to provide users with a complete picture of firewalls and relationships among them for error debugging and anomaly removal. In addition, in this paper, we also enumerate the source of security inconsistency while setting ACLs and make use of it as a basis of the design of our visualization model. Currently, part of the firewall configuration of our campus network has been used as our system's input to demonstrate our system's implementation.
Keywords: Defense in depth; Firewall security consistency; System visualization; Rule anomalies; Behavior mismatching
An interactive virtual guide for the AR based visit of archaeological sites BIBAKFull-Text 415-425
  Andrea F. Abate; Giovanni Acampora; Stefano Ricciardi
One of the most interesting research lines about avatars is the design and the implementation of a synthetic behaviour able to drive avatar's actions according to an adaptive interaction paradigm. This aspect, indeed, is of fundamental importance to many advanced applications involving avatars and humans. This study presents a novel framework exploiting augmented reality to visualize a synthetic 3D virtual guide inside an exhibit or a public gallery, to assist visitors wearing a Head Mounted Display during their visit and providing them with both visual and informative enhancements not available in a standard tour. The Human-avatar interaction is approached through a model based on timed automata to address the conversational issues and to improve the quality of interaction by means of an effective synchronization. A usability study conducted on an application of this research to the "avatar assisted tour" of a roman villa, confirms the efficacy of the approach.
Keywords: Human-avatar interaction; Augmented reality; Virtual characters in real environments; Behavioural animation
A general method for drawing area-proportional Euler diagrams BIBAKFull-Text 426-442
  Gem Stapleton; Peter Rodgers; John Howse
Area-proportional Euler diagrams have many applications, for example they are often used for visualizing data in medical and biological domains. There have been a number of recent research efforts to automatically draw Euler diagrams when the areas of the regions are not considered, leading to a range of different drawing techniques. By contrast, substantially less progress has been made on the problem of automatically drawing area-proportional Euler diagrams, although some partial results have been derived. In this paper, we considerably advance the state-of-the-art in area-proportional Euler diagram drawing by presenting the first method that is capable of generating such a diagram given any area-proportional specification. Moreover, our drawing method is sufficiently flexible that it allows one to specify which of the typically enforced well-formedness conditions should be possessed by the to-be-drawn Euler diagram.
Keywords: Area-proportional; Euler diagrams; Information visualization; Non-hierarchical data visualization; Venn diagrams
A visual language for the creation of narrative educational games BIBAKFull-Text 443-452
  Eugenio J. Marchiori; Ángel del Blanco; Javier Torrente; Iván Martinez-Ortiz; Baltasar Fernández-Manjón
This paper presents a DSVL that simplifies educational video game development for educators, who do not have programming backgrounds. Other solutions that reduce the cost and complexity of educational video game development have been proposed, but simple to use approaches tailored to the specific needs of educators are still needed. We use a multidisciplinary approach based on visual language and narrative theory concepts to create an easy to understand and maintain description of games. This language specifically targets games of the adventure point-and-click genre. The resulting DVSL uses an explicit flow representation to help educational game authors (i.e. educators) to design the story-flow of adventure games, while providing specific features for the integration of educational characteristics (e.g. student assessment and content adaptation). These highly visual descriptions can then be automatically transformed into playable educational video games.
Keywords: Domain-specific visual language; Educational video games; Serious games; Educators; Story-flow; Game authoring
Exploiting clustering approaches for image re-ranking BIBAKFull-Text 453-466
  Daniel Carlos Guimarães Pedronette; Ricardo da S. Torres
This paper presents the Distance Optimization Algorithm (DOA), a re-ranking method aiming to improve the effectiveness of Content-Based Image Retrieval (CBIR) systems. DOA considers an iterative clustering approach based on distances correlation and on the similarity of ranked lists. The algorithm explores the fact that if two images are similar, their distances to other images and therefore their ranked lists should be similar as well. We also describe how DOA can be used to combine different descriptors and then improve the quality of results of CBIR systems. Conducted experiments involving shape, color, and texture descriptors demonstrate the effectiveness of our method, when compared with state-of-the-art approaches.
Keywords: Content-based image retrieval; Re-ranking; Distance optimization; Clustering