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73INFORMATION VISUALIZATION IN THE INTERACTIONWITH IDLMaria Francesca Costabile and Giovanni SemeraroDipartimento di Informatica, Università di BariVia Orabona 4, 70125 Bari, Italycostabile, semeraro@di.uniba.itAbstractWe briefly discuss the state of the art of the research in information visualization. Then, we describe atechnique for visualizing meta-information about the content of a networked information system in thecontext of a digital library, which is being developed at the University of Bari.1. Introduction and MotivationThe computer technology is providing everybody the possibility of directly exploring informationresources. Huge amount of data are becoming available on networked information systems, rangingfrom unstructured and multimedia documents to structured data stored in databases. On the one side,this is extremely useful and exciting. On the other side, the ever growing amount of information atdisposal generates cognitive overload and even anxiety, especially in novice or occasional users.Nowadays, wide varieties of users access, extract, and display information that is distributed onvarious sources, which differ in type, form and content. The current user interfaces are usually toodifficult for novice users and/or inadequate for experts, who need tools with many options, thuslimiting the actual power of the computer. Users need to easily understand what kind of objects arestored in the available sources they have access to, how they can retrieve and organize them alongways that permit to make rapid decisions on what is relevant and which patterns exist among objects.Users also need to manipulate the retrieved information in order to incorporate it in their specific tasks.As a consequence, networked information systems must provide enhanced user interfaces that supportthis intensive interaction between users and information.In this context, the conventional interfaces, based on the view of information retrieval as anisolated task in which the user formulates a query against a homogeneous collection to obtain matchingdocuments, are completely out of date. Indeed, this view does not correspond for several reasons to thereality of users working with networked information systems. For example, users are often unable toformulate specific questions, and they realize what they are trying to ask and how to ask it by browsingthe system. This process has been called progressive querying in [CCL94] and iterative queryrefinement in [RPH95]. Moreover, users often consult multiple sources with different contents, forms,and methods of access.The same holds for searching in structured relational database system, for which the SQL languagehas become a widespread standard. With SQL, users perform queries that specify matches on attributevalues, such as author, publisher, date of publication. Each document has values for the attributes, anddatabase management methods enable rapid retrieval even with millions of documents. Although SQLis a standard, many form-fillin variants for expressing relational database queries have been proposedto aid novice searchers. However, the diversity is itself an impediment to ease of use. Designers musttake into account that users of walk-up kiosks or WWW pages cannot invest hours or minutes to learneach interface. Finding a way to provide powerful search without overwhelming novice users is acurrent challenge.We recognize three different needs of people exploring information: 1) to understand the content ofthe information system, 2) to extract the information of interest, and 3) to browse the retrievedinformation in order to verify that it matches what they wanted. To satisfy such needs, the user-interface designers are challenged to invent more powerful search techniques, simpler query facilities,and more effective presentation methods. When creating new techniques, we have to keep in mind thevariability of the user population, ranging from first time or occasional versus frequent users, fromtask-domain novices versus experts, from naive (requesting very basic information) versussophisticated users (interested in very detailed and specific information). Since there is not a technique