3D Content-Based Visualization of Databases Anestis KOUTSOUDIS Dept. of Electrical and Computer Engineering, Democritus University of Thrace 12 Vas. Sofias Str., Xanthi, 67100, Greece Fotis ARNAOUTOGLOU Cultural and Educational Technology Institute, Research Centre “Athena” 58 Tsimiski Str., Xanthi, 67100, Greece George PAVLIDIS Cultural and Educational Technology Institute, Research Centre “Athena” 58 Tsimiski Str., Xanthi, 67100, Greece and Christodoulos CHAMZAS Dept. of Electrical and Computer Engineering, Democritus University of Thrace 12 Vas. Sofias Str., Xanthi, 67100, Greece ABSTRACT The scope of this paper is to propose an innovative interactive system for 3D visualization of multimedia databases. In such databases, the digital content is accompanied by complementary information and metadata that describe the content. The pro- posed 3D visualization environment is able to provide multi- scale representations driven by appropriate clustering processes that exploit content descriptions. It is also able to provide direct access to all the digital content, both in terms of physical access to the multimedia files as well as in terms of searching and re- trieving information. Keywords: 3D graphical user interface, 3D visualization, con- tent-based description, content-based visualization. 1. INTRODUCTION As the 3D technologies become more and more common to the wide public and gain even more attention, acceptance and ap- preciation, there is an increasing demand for more sophisticated user interfaces that can use metaphors of real life and keep the user far apart from low level information and data structures. Nowadays, users prefer to access data in a more human-oriented and comprehensive way instead of using typical text-based in- terfaces. Additionally, there is an increasing demand for inter- faces that reflect the content of the data and are able to provide content-based retrieval mechanisms and representations. These facts are complemented by a continuous development of 3D display hardware, based on both active and passive technolo- gies, that contribute on the generation of an open field for re- search and development of new human-computer interaction interfaces on both algorithmic and software levels. The system described in this work is an innovative interactive 3D visualization system, and it is actually a proposal for future user interfaces and front-end virtual environments for multime- dia and multi-dimensional databases, such as image databases, video archives, musical archives and collections. The digital content is usually accompanied by complementary information and metadata that describe its content. The procedures of extrac- tion and insertion of the accompanied information in the data- base is not a subject of this work. We focus mainly on the 3D visualization environment that is able to perform multiscale representations and direct access to the whole digital dataset. The system provides a virtual 3D space based on taxonomies either on high or low level features retrieved from basic catego- ries and sub-categories. More specifically, the proposed ap- proach performs 3D data clustering and visualization according to metadata and content-based descriptions that have already been extracted and stored within the archive. The system is composed by two main sub-systems: • the clustering sub-system, which uses Self-Organizing Maps (SOM) [1]-[3] to cluster the data and construct the 3D virtual space in terms of 3D coordinates derived from the data, and • the visualization and user interaction sub-system, which uses features of the OpenGL graphics libraries to render in real-time the virtual space and provide the user with the required interactivity For the evaluation of the proposed system we considered as a music archive of Greek traditional songs. The clustering sub- system was trained and evaluated using a collection of Greek traditional music database that was formed in CETI as a part of a national R&D project named “Polymnia”, containing about 1000 files. The collection follows an XML native database for- mat and includes the whole dataset that includes information such as: • links to digital musical files and audio samples • accompanied information (such as scores, refer- ences, analysis work) and • metadata (such as the genre, the beat and the meter, or other automatically extracted low level charac- teristics). 2. DATA VISUALIZATION IN THREE DIMENSIONS It is a fact that during the last decade, an increase in the volume and complexity of the digital information has occurred. As a result, more advanced techniques are now required in order to