Stefan Negru

Visualizing ontologies with VOWL

The Visual Notation for OWL Ontologies (VOWL) is a well-specified visual language for the user-oriented representation of ontologies. It defines graphical depictions for most elements of the Web Ontology Language (OWL) that are combined to a force-directed graph layout visualizing the ontology. In contrast to related work, VOWL aims for an intuitive and comprehensive representation that is also understandable to users less familiar with ontologies. This article presents VOWL in detail and describes its implementation in two different tools: ProtegeVOWL and WebVOWL. The first is a plugin for the ontology editor Protege, the second a standalone web application. Both tools demonstrate the applicability of VOWL by means of various ontologies. In addition, the results of three user studies that evaluate the comprehensibility and usability of VOWL are summarized. They are complemented by findings from an interview with experienced ontology users and from testing the visual scope and completeness of VOWL with a benchmark ontology. The evaluations helped to improve VOWL and confirm that it produces comparatively intuitive and comprehensible ontology visualizations.

VOWL 2: User-Oriented Visualization of Ontologies

Ontologies become increasingly important as a means to structure and organize information. This requires methods and tools that enable not only ontology experts but also other user groups to work with ontologies and related data. We have developed VOWL, a comprehensive and well-specified visual language for the user-oriented representation of ontologies, and conducted a comparative study on an initial version of VOWL. Based upon results from that study, as well as an extensive review of other ontology visualizations, we have reworked many parts of VOWL. In this paper, we present the new version VOWL 2 and describe how the initial definitions were used to systematically redefine the visual notation. Besides the novelties of the visual language, which is based on a well-defined set of graphical primitives and an abstract color scheme, we briefly describe two implementations of VOWL 2. To gather some insight into the user experience with the new version of VOWL, we have conducted a qualitative user study. We report on the study and its results, which confirmed that not only the general ideas of VOWL but also most of our enhancements for VOWL 2 can be well understood by casual ontology users.

WebVOWL: Web-based Visualization of Ontologies

We present WebVOWL, a responsive web application for the visualization of ontologies. It implements the Visual Notation for OWL Ontologies (VOWL) and is entirely based on open web standards. The visualizations are automatically generated from JSON files, into which the ontologies need to be converted. An exemplary OWL2VOWL converter implemented in Java and based on the OWL API is currently used for this purpose. The ontologies are rendered in a force-directed graph layout according to the VOWL specification. Interaction techniques allow to explore the ontologies and customize their visualizations.

The ProtégéVOWL Plugin: Ontology Visualization for Everyone

The Visual Notation for OWL Ontologies (VOWL) provides a visual language for the representation of ontologies. In contrast to related work, VOWL aims at an intuitive and interactive visualization that is also understandable to users less familiar with ontologies. This paper presents ProtegeVOWL, a first implementation of VOWL realized as a plugin for the ontology editor Protege. It accesses the internal ontology representation provided by the OWL API and defines graphical mappings according to the VOWL specification. The information visualization toolkit Prefuse is used to render the visual elements and to combine them into a force-directed graph layout. Results from a preliminary user study indicate that ProtegeVOWL does indeed provide a comparatively intuitive and usable ontology visualization.

Towards a unified visual notation for OWL ontologies: insights from a comparative user study

Browsing ontologies and making sense of their concepts and relationships are important activities in knowledge engineering. They are supported by a large number of tools that often provide visual representations of the ontologies for better illustration. However, different notations are used to represent the ontologies which can be confusing when switching tools. Furthermore, many representations provide only basic overviews of the ontologies that are not sufficient to get a deeper understanding of the concepts and relationships. A unified visual notation for OWL ontologies would be most helpful to overcome these limitations. Having this goal in mind, we compare two different notations for OWL ontologies in this paper: the UML profile of the Ontology Definition Metamodel (ODM) and the Visual Notation for OWL Ontologies (VOWL). We report on a comparative user study of these notations and discuss benefits and limitations raised by the study participants. Based on these findings, we draw some general conclusions regarding the development of a unified visual notation for OWL ontologies.

A conceptual architecture of an arduino-based social-emotional interactive system

This paper presents an open system that focuses on the social and emotional aspects of the human-computer interaction. We describe a conceptual architecture for an interactive system that can collect, identify and operate with a users emotions in a social environment. We identified important issues in building and using such a system and provided solutions for those issues, so that it can be successfully implemented. Several use cases are brought into discussion.

OntoViBe 2: Advancing the Ontology Visualization Benchmark

A variety of ontology visualizations have been presented in the last couple of years. The features of these visualizations often need to be tested during their development or for evaluation purposes. However, in particular for the testing of special concepts and concept combinations, it can be difficult to find suitable ontologies. We have developed OntoViBe, an ontology covering a wide variety of OWL language constructs for the purpose of testing ontology visualizations. This paper presents OntoViBe 2, which extends the first version by annotations, individuals, anonymous classes, and a module for testing different combinations of cardinality constraints, among others. We describe the design principles underlying OntoViBe 2 and present the supported features in a coverage matrix. Finally, we load OntoViBe 2 with ontology visualization tools and point to some noteworthy aspects of the respective visualizations that become apparent and demonstrate how OntoViBe can be used for testing ontology visualizations.

Towards a conceptual model for describing the personas methodology

In the field of Human-Computer Interaction, the Personas methodology is used to communicate the users preferences, goals, frustrations and requirements. Although a widely used method, little progress has been made in creating a personas model. This paper aims to provide such a conceptual model, which includes concepts and properties used in the personas methodology, via an OWL specification.

Towards a Visual Notation for OWL: A Brief Summary of VOWL

The Web Ontology Language OWL has no standardized visual notation in contrast to related modeling languages. However, the visual representation of individual and combined OWL elements as well as complete OWL ontologies can be very useful in many cases. We have developed the Visual Notation for OWL VOWL that defines graphical representations for most of the OWL language constructs. In contrast to related work, VOWL aims at a complete and well-specified notation that is easy to understand and implement. This paper reports on the current state of development and briefly describes the main design principles and considerations. At OWLED 2015, we conducted a special session to gather feedback on how to further improve the visual notation and to collect requirements for its future development.

An Educational Tool for an Interactive Faceted Exploration of DBpedia Life Sciences Data

As the volume of information on the Web and the number of Linked Open Data sources increase considerably, users need easy to use Web-based tools and applications to help them navigate, interpret and make use of the available information/data. In this context, we introduce RDFSpecies, as an educational tool for interactive exploration of Semantic Web data. Our approach is targeted at users that have no experience or little knowledge of RDF model and Semantic Web technologies. We make use of different interaction metaphors to aid them in navigating, exploring and visualizing DBpedia data.