REQUIREMENTS FOR INTERACTIVE ONTOLOGY VISUALIZATION Using Hypertree +2.5D Visualization for Exploring Relationships between Concepts Isabel Cristina Siqueira da Silva 1,2 and Carla Maria Dal Sasso Freitas 1 1 Instituto de Informática, UFRGS, Av. Bento Gonçalves, 9500, Porto Alegre, RS, Brazil 2 Faculdade de Informática, Centro Universitário Ritter dos Reis, UNIRITTER Rua Orfanotrófio, 555, Porto Alegre, RS, Brazil Keywords: Visualization, Ontology, Interaction. Abstract: Ontologies are used for sharing among people or software agents the common understanding of the information structure in a certain domain. Usually, ontologies are represented as static 2D graphs where the relationships are displayed as edges, which often overlap and cause cognitive overload. Three-dimensional representations can also lead to confusion due to occlusion. Moreover, as the ontology grows, incorporating new concepts (and their relationships) increases the visualization complexity either in 2D or in 3D. In this paper, we present a study about the requirements of visualization and interaction with ontologies. In order to do that, we interviewed with four experts on ontology creation and use. From the results, we propose the design of a 2.5D visualization tool for exploring relationships between ontology concepts. 1 INTRODUCTION There is a gradual increase of information available and efficient methods for information retrieval are necessary in order to allow interoperability and cooperation between several databases. Data semantics is the more traditional approach for data integration because it focuses on the relationship between data. As such, ontologies define concepts and ensure interoperability between systems. In his work, Sowa (2005) points out that ontology is the study of the categories of things that exist or may exist in some domain, i.e., it is a catalogue of the types of things that are assumed to exist in a domain of interest D from the perspective of a person who uses a language L for the purpose of talking about D. According to Gruber (1996), ontology is a formal and explicit specification of a conceptualization. Noy and McGuiness (2001) discuss that ontologies allow sharing the common understanding of the structure of information among people or software agents. Ontologies separate domain knowledge from the operational knowledge, make domain assumptions explicit and enable reuse. However, due to the specificities of the concepts expressed in ontologies, the analysis of individual relationships is complex. Thus, interactive ontology visualizations need to be efficient and allow rapid comprehension of concepts and relationships. Katifori (2007) confirms that it is not simple to create a visualization that displays effectively all the information, and, at the same time, allows the user to perform easily various operations on the ontology. Then, the challenge is to define the best way to represent relationships between categorized concepts mainly because each concept can have a number of related attributes. This work presents requirements analysis for visualization and interaction in tools aiming at creating, manipulating and exploring ontologies. We conducted interviews with users who work with ontologies and conceptual modelling. From these results, we present an initial design of a 2.5D ontology visualization method that aims at systematizing and transmitting knowledge more efficiently. The text is organized as follows. Section 2 discusses related work. Section 3 presents the user interviews and points out requirements for ontology visualization tools. Section 4 presents our proposal for ontology visualization. Results are discussed and final comments are drawn in Section 5. 242 Siqueira da Silva I. and Dal Sasso Freitas C.. REQUIREMENTS FOR INTERACTIVE ONTOLOGY VISUALIZATION - Using Hypertree +2.5D Visualization for Exploring Relationships between Concepts . DOI: 10.5220/0003372402420248 In Proceedings of the International Conference on Imaging Theory and Applications and International Conference on Information Visualization Theory and Applications (IVAPP-2011), pages 242-248 ISBN: 978-989-8425-46-1 Copyright c  2011 SCITEPRESS (Science and Technology Publications, Lda.)