Citiviz: A Visual User Interface to the CITIDEL System Nithiwat Kampanya, Rao Shen, Seonho Kim, Chris North, Edward A. Fox Computer Science Department, Virginia Tech, Blacksburg, VA 24061 USA {nkampany, rshen, shk, north, fox}@vt.edu Abstract. The Digital Library (DL) field is one of the most promising areas of application for information visualization technology. In this paper, we propose a visual user interface tool kit for digital libraries, to deliver an overview of document sets, with support for interactive direct manipulation. Our system, Citiviz, employs a dynamic hyperbolic tree to display hierarchical relationships among documents, based on where their topics fit into the ACM classification system. Also, Citiviz provides an interactive, animated 2-dimensional scatter plot. With it, users may gain insight by changing various parameters, or may directly jump to a particular document based on its label or location. According to a preliminary evaluation, our system shows advantages in performance and user preference relative to traditional text based DL web interfaces. 1 Introduction The Computing and Information Technology Interactive Digital Educational Library (CITIDEL, http://www.citidel.org), part of the NSDL (National Science Digital Library, http://www.nsdl.org), uses OAI-PMH (the Open Archives Initiative Protocol for Metadata Harvesting) to harvest resource metadata from its member collections. Those member collections are other digital libraries (DLs) that share their resources with CITIDEL, which provides integrated browsing and searching services. Users can browse separately through each member collection, or can browse through the union collection using any of four different classification schemes. Nevertheless, the primary means to access CITIDEL is through searching. Unfortunately, if users are unfamiliar with the topic of their search, or lack experience regarding search tactics, relevant documents may only appear frustratingly far down in a ranked list of search results. Fortunately, visual interfaces to DLs apply powerful data analysis and information visualization techniques to generate visualizations of document collections in DLs, with possible beneficial effect on browsing and searching. Thus, we have integrated text mining and information visualization to develop a visual interface to CITIDEL. Visualization techniques of one broad category consider predefined document attributes, such as author or date, and query relevance. One example is the Envision interface [17, 25]. It can organize search results according to metadata along the X and Y-axes, and show values for attributes associated with retrieved documents within each cell. However, the view provided by the original version of the Envision