Flexible Search and Navigation using Faceted Metadata

We have developed an innovative search interface that allows non-expert users to move through large information spaces in a flexible manner without feeling lost. The design goal was to offer users a “browsing the shelves” experience seamlessly integrated with focused search. Key to achieving our goal is the explicit exposure of hierarchical faceted metadata in a manner that is intuitive and inviting to users. After several iterations of design and testing, the usability results are strikingly positive. We believe our approach marks a major step forward in search user interfaces and can serve as a model for web-based collections of up to 100,000 items.  Search User Interfaces, Faceted Metadata  Although general Web search is steadily improving [30], studies show that search is still the primary usability problem in web site design. A recent report by Vividence Research analyzing 69 web sites found that the most common usability problem was poorly organized search results, affecting 53% of sites studied. The second most common problem was poor information architecture, affecting 32% of sites . Studies of search behavior reveal that good search involves both broadening and narrowing of the query, appropriate selection of terminology, and the ability to modify the query [31]. Still others show that users often express a concern about online search systems since they do not allow a “browsing the shelves” experience afforded by physical libraries [6] and that users like wellstructured hyperlinks but often feel lost when navigating through complex sites [23]. Our goals are to support search usability guidelines [28], while avoiding negative consequences like empty result sets or feelings of being lost. We are especially interested in large collections of similar-style items (such as product catalog sites, sites consisting of collections of images, or text documents on a topic such as medicine or law). Our approach is to follow iterative design practices from the field of human-computer interaction [29], meaning that we first assess the behavior of the target users, then prototype a system, then assess that system with target users, learn from and adjust to the problems found, and repeat until a successful interface is produced. We have applied this method to the problem of creating an information architecture that seamlessly integrates navigation and free-text search into one interface. This system builds on earlier work that shows the importance of query previews [25] for indicating next choices (thus allowing the user to use recognition over recall) and avoiding empty result sets. The approach makes use of faceted hierarchical metadata (described below) as the basis for a navigation structure showing next choices, providing alternative views, and permitting refinement and expansion in new directions, while at the same time maintaining a consistent representation of the collection’s structure . This use of metadata is integrated with free-text search, allowing the user to follow links, then add search terms, then follow more links, without interrupting the interaction flow. Our most recent usability studies show strong, positive results along most measured variables. An added advantage of this framework is that it can be built using off-the-shelf database technology, and it allows the contents of the collection to be changed without requiring the web site maintainer to change the system or the interface. For these reasons, we believe these results should influence the design of information architecture of information-centric web sites. In the following sections we define the metadata-based terminology, describe the interface framework as applied to a collection of architectural images, report the results of usability studies, discuss related work, and discuss the implications of these results.  METADATA Content-oriented category metadata has become more prevalent in the last few years, and many people are interested in standards for describing content in various fields (e.g., Dublin Core and the Semantic Web). Web directories such as Yahoo and the Open Directory Project are familiar examples of the use of metadata for navigation structures. Web search engines have begun to interleave search hits on category labels with other search results. Many individual collections already have rich metadata assigned to their contents; for example, biomedical journal articles have on average a dozen or more content attributes attached to them. Metadata for organizing content collections can be classified along several dimensions: • The metadata may be faceted, that is, composed of orthogonal sets of categories. For example, in the domain of architectural images, some possible facets might be Materials (concrete, brick, wood, etc.), Styles (Baroque, Gothic, Ming, etc.), View Types, People (architects, artists, developers, etc.), Locations, Periods, and so on. • The metadata (or an individual facet) may be hierarchical (“located in Berkeley, California, United States”) or flat (“by Ansel Adams”). • The metadata (or an individual facet) may be singlevalued or multi-valued. That is, the data may be constrained so that at most one value can be assigned to an item (“measures 36 cm tall”) or it may allow multiple values to be assigned to an item (“uses oil paint, ink, and watercolor”). We note that there are a number of issues associated with creation of metadata itself which we are not addressing here. The most pressing problem is how to decide which descriptors are correct or at least most appropriate for a collection of information. Another problem relates to how to assign metadata descriptors to items that currently do not have metadata assigned. We will not be addressing these issues, in part because many other researchers already are, and because the fact remains that there are many existing, important collections whose contents have hierarchical metadata already assigned.  We are particularly concerned with supporting non-professional searchers in rich information seeking tasks. Specifically we aim to answer the following questions: do users like and understand flexible organizations of metadata from different hierarchies? Are faceted hierarchies preferable to single hierarchies? Do people prefer to follow category-based hyperlinks or do they prefer to issue a keyword-based query and sort through results listings? 1http://dublincore.org, http://www.w3.org/2001/sw 2http://www.yahoo.com, http://dmoz.org  The opening page for both interfaces shows a text search box and the first level of metadata terms. Hovering over a facet name yields a tooltip (here shown below Locations) explaining the meaning of the facet. Before developing our system, we tested the idea of using hierarchical faceted metadata on an existing interface that exemplified some of our design goals. This preliminary study was conducted using a commercial recipe web site called Epicurious containing five flat facets, 93 metadata terms, and approximately 13,000 recipes. We compared the three available search interfaces:(1) Simple keyword search, with unsorted results list (2) Enhanced search form that exposes metadata using checkboxes and drop-down lists, with unsorted results list. (3) Browse interface that allows user to navigate through the collection, implicitly building up a query consisting of an AND across facets; Selecting a category within a facet (e.g., Pasta within Main Ingredient) narrows results set, and users are shown query previews at every step. In the interests of space, we can only provide a brief summary of this small (9 participant) study: All the participants who liked the site (7 out of 9) said they were likely to use the browse interface again. Only 4 said this about enhanced search and 0 said this about simple search. Participants especially liked the browse interface for open-ended tasks such as “plan a dinner party.” We took this as encouraging support for the faceted metadata approach. However, the recipe browse facility is lacking in several ways. Free-text search is not integrated with metadata browse, the collection and metadata are of only moderate size, and the metadata is organized into flat (non-hierarchical) facets. Finally users are only allowed to refine queries, they cannot broaden 3http://eat.epicurious.com/recipes/browse home/