ERELT: A Faster Alternative to the List-Based Interfaces for Tree Exploration and Searching in Mobile Devices Abhishek P. Chhetri Computer Engineering Program Erik Jonsson School of Engineering and Computer Science University of Texas at Dallas Richardson, TX 65080-3021, USA achhetri@utdallas.edu Kang Zhang School of Software Engineering Tianjin University, Tianjin, China Department of Computer Science University of Texas at Dallas Richardson, TX 65080-3021, USA kzhang@utdallas.edu Eakta Jain Texas Instruments Dallas TX, USA, Department of Computer Science University of Texas at Dallas Richardson, TX 65080-3021, USA eakta.jain@gmail.com ABSTRACT This paper presents ERELT (Enhanced Radial Edgeless Tree), a tree visualization approach on modern mobile devices. ERELT is designed to offer a clear visualization of any tree structure with intuitive interaction. We are interested in both the observation and navigation of such structures. Such visualization can assist users in interacting with a hierarchical structure such as a media collection, file system, etc. In the ERELT visualization, a subset of the tree is displayed at a time. The displayed tree size depends on the maximum number of tree elements that can be put on the screen while maintaining clarity. Users can quickly navigate to the hidden parts of the tree through touch-based gestures. We conducted a user study to evaluate this visualization for a music collection. Test results show that this approach reduces the time and effort in navigating tree structures for exploration and search tasks. Categories and Subject Descriptors H.5.2 [User Interfaces]: Graphical user interface (GUI), H.1.2 [User/Machine Systems]: Human factors, I.3.6 [Methodology and Techniques]: Interaction Techniques General Terms Algorithms, Design, Human Factors Keywords Hierarchy Visualization, Mobile Devices, Navigation, RELT (Radial Edgeless Tree), User Interface 1. INTRODUCTION Current market trends show strong rise in smartphones and tablets. Smartphones can now match the processing capabilities of laptop/PCs from a few years ago with a fraction of the power usage. With emails, contacts, documents, pictures and music all stored in the cloud, one no longer needs to sit in front of a personal computer to access data. There are, however, still many challenges in mobile computing, such as smaller screens and lack of separate input devices such as keyboard. Although the screen resolution in mobile devices has been increasing, in terms of screen size they are still much smaller than laptops/PC monitors. This makes it difficult to present tabular and hierarchical structures in mobile device when a large proportion of application data are hierarchical in nature. For example, a file system is a hierarchical structure, and a file list within a folder is usually displayed in tabular format. A multimedia collection such as music, pictures, videos, etc. may exist in hierarchical structures, and is usually displayed in tabular form in laptops/PCs. Apart from the presentation issues, how we interact with these data structures in mobile devices is also challenging. Modern mobile devices are mostly equipped with touch screens, and soft keyboards. Any keyboards or buttons displayed on screen take space, which is already at a premium. Thus, it is necessary to come up with intuitive methods of interaction without sacrificing screen area for input. Most hierarchical structures are represented by lists in mobile devices. Lists offer fast interaction but can only display single level under one node at a time. This paper presents a technique for visualizing and navigating hierarchical structures on mobile devices that focuses on the two issues presented above. 1. Maximal utilization of screen area to display hierarchical structures. 2. Intuitive interaction mechanism that allows rapid navigation and exploration of the structures. The research aims to utilize the screen estate to display maximum possible information, without sacrificing clarity. The objective is to use touch technology in most modern smartphones to implement gesture based commands that are intuitive and mimic real-world object interactions. The paper presents further enhancement over our earlier prototype [1], and a user study using media player application utilizing ERELT. Our user study shows that ERELT supports faster exploration of tree structures than traditional list based interfaces. To date, considerable research has been done in the areas of information visualization and human-computer interaction (HCI). While many of these researches have produced a variety of visualization techniques for hierarchical structures, little previous work has focused on utilizing visualization as UI elements. Our contribution is a hierarchy visualization technique for small screens with a practical approach for user interaction. We extensively evaluate the ease of user interaction with the proposed ERELT visualization through a user study. Our results show that it takes significantly less time and fewer number of Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Permissions@acm.org. VINCI '13, August 17 - 18 2013, Tianjin, China Copyright 2013 ACM 978-1-4503-1988-1/13/08…$15.00. http://dx.doi.org/10.1145/2493102.2493109 54