Search Interfaces for Handheld Mobile Devices
George Buchanan & Matt Jones
Computing Science, Middlesex University, UK
IntroductionHandheld computers, Web-phones and other mobile devices will be key components in the ongoing trend towards a pervasive Web. To meet the needs of the many millions of users who might access the Web using these devices effective user interfaces need to be developed.
Handheld browsers have very different interaction characteristics to their desktop counterparts and these have to be considered by those working on the standards and content for the platforms. In earlier work  we proposed some design features for navigating a site using small screen devices and demonstrated their efficacy with a prototype tool . This tool is now being extended to consider the issues related to searching.
Good direct search-based methods of finding information will be vital to handheld users . Small screen users show a significant preference for direct access methods: they select 'search' options much more frequently than large screen users and do not follow long browsing paths.
Most conventional search engine interfaces present search output as scrollable lists. Users finds these sorts of display difficult even on large screens; scrolling a long list within a very small screen is likely to lead to ineffectiveness and errors. There is a need, then, to develop ways of visualising and manipulating the output of search in the limited display areas available.
Visualising Search OutputWebTwig  presents an outline view of a Web site. The aim is to improve users' ability to find topics of interest by reducing the cost of exploring a site: users can identify potentially useful areas of a site without having to negotiate page-after-page. Our initial evaluations suggested potential gains  and these results have been recently amplified by work done by another group .
Search queries typically return hundreds of potential hits. Making sense of such output is difficult. Various methods of visualising search results have been proposed. Many of the approaches (for a review see ) which include WebBook which uses a 3D display to organise information and TileBars which uses graphics to communicate relevance and structural information are inappropriate to the handheld environment. These methods rely on display capabilities that are not viable with handhelds.
As we demonstrated with our earlier WebTwig work, though, it is possible to present helpful, structural information using a simple text-based display. The first version of WebTwig provides a framework for one sort of direct access: users can focus on information by repeatedly expanding nodes in the tree view. In our new prototype, we have maintained the outline-view approach to present the results of an explicit search process. Users enter their search terms and when the search is completed, the top-level nodes of the portions of the tree that contain the hits are shown to the user. Users can then progressively open up these views to explore the alternative hit possibilities (see figure 1). The outline view not only limits the amount of scrolling required to make sense of the search results but provides context information which should help users make decisions about which alternatives to pursue.
Figure 1. WebTwig prototype search interface for handheld browser. User entered search term "animal". User was then presented with list of top level nodes that contained hits (e.g., 'education'). By expanding nodes that contain hits, the user can progressively gain information on the context of hit. The prototype also allows the full path to a hit to be shown with one click.
Ongoing WorkWe are in the process of evaluating our new search facilities to see whether they actually improve users' performance and acceptance. In addition we are looking at an alternative method. Our outliner view of search results will fail if the site does not have a meaningful structure that can be automatically extracted by WebTwig. There are several clustering algorithms (e.g. ) that could be used to organise search results in these cases; limited trials indicate that for large screen displays there may be some usability benefits . We are implementing a clustering algorithm and will compare a cluster-based interface for handheld interaction with the outline view for a range of Web site types.
- Buyukkokten, O., Garcia-Molina H., Paepcke, A. & Winograd, T. (2000). Power Browser: Efficient Web Browsing for PDAs. To appear, Proceedings ACM CHI Conference, Hague, April 2000.
- Hearst, M. (1997). Interfaces for searching the Web. Scientific American, March 1997.
- Jones, M., Marsden, G., Mohd-Nasir, N., Boone K. & Buchanan, G. (1999). Improving Web interaction on small displays. Proceedings of W8 conference, Toronto, May 1999 (Also reprinted in International Journal of Computer and Telecommunications Networking, 3 (1999), 1129-1137).
- Jones, M., Marsden, G, Mohd-Nasir, N. & Buchanan, G. (1999), A site-based outliner for small screen web access. Poster Proceedings of W8 conference, Toronto, May 1999.
- Jones M, Mohd-Nasir, N & Buchanon, G (1999). Evaluation of WebTwig - a site outliner for handheld Web access. International Symposium on Handheld and Ubiquitous Computing, Karlsrhue, Germany, September 1999. Lecture Notes in Computer Science 1707, Gellerson, H-W (Ed.), pp343-345, Springer-Verlag.
- Pirolli, P., Schank, P., Hearst, M. & Diel, C. (1996). Scatter/Gather browsing communicates topic structure of a very large text collection. Proceedings ACM CHI Conferencce 1996.
- Zamir, O. & Etzioni, O. (1999). Grouper: a dynamic clustering interface to Web search results. Proceedings of W8 conference Toronto, May 1999, pp. 283-296,