SEARCH

The problem of locating items in libraries is frequently referred to as "search," although that word tends to imply that one knows in advance what one is looking for, and possesses handles, indicators or index terms to serve as finding aids. This narrow view ignores the activity of browsing or even the higher-level function of becoming acquainted in general with a library's holdings. Browsing in a traditional library is a physical activity-it involves scanning shelves on which related works have been placed in proximity, and occasionally withdrawing them from the shelves for examination. Browsing in a digital library is a logical activity mediated by a computer. It does not require physical proximity in any sense; indeed, two consecutive items examined may be stored on different continents. The question, then, is how can a library user (not to say the library staff) become familiar with the whole of recorded human information in a way that makes it accessible and useful?

We adopt the term "navigation" to mean moving about in a digital collection. Search is a directed form of navigation in which the goal is defined in advance with reasonable clarity. The result of a search may be an item, a collection of items, or any part of an item, even down to a single glyph. Tools must be provided that enable users to move about at varying levels of granularity within the corpus.

The usual requirement for a search is that the user is looking for a specific piece of information or a summary of what is available about a certain topic. A common case is that the user wants the answer to a specific question, such as when the postcard was invented. Only rarely does such a question translate naturally into a keyword query. Such retrieval is indirect in the sense that the user wants to learn A, but formulates a query B, to which he receives a set of retrieved documents that must be scanned to determine whether the answer to A is among them. It would be far better simply to allow the user to ask question A instead of requiring him to convert it to some query language.

Non-Textual Matter

The existence of Web searchers proves that text can be searched without being indexed or cataloged. At least on a microscopic level, documents can be located purely by their content. Many documents consist of text plus other information such as mathematical equations, tables and drawings that themselves cannot be searched directly but can often be located by the presence of related text. Purely non-textual matter is very different. Although substantial progress is being made on video searching (through the use of extensive captioning cues, speech recognition and other aids), content searching of music and visual materials is non-existent or in its infancy. The problem is further complicated by the existence of work that combines media in various ways.

Translingual Issues

Most library items, particularly in non-English-speaking countries, are not in English. The central translingual library question is how users may navigate through materials in foreign languages and make effective use of them. Translingual search is currently a research problem for which obvious solutions do not work. A keyword search cannot be made multilingual merely by translating the keywords one at a time. The number of possible translations of each word may be very large, so an explosion in the number of hits may result. This approach also takes no account of idiomatic uses, untranslatable words such as particles, and numerous other language-related phenomena.

An interim solution is the use of translation assistants-programs that offer dictionary entries or partial or suggested translations of text portions. These show great promise for users who are at least partially familiar with the language of the retrieved document.

Synthetic Text

A user who is looking for general information on a particular topic is constrained in traditional libraries to go to an encyclopedia (which may have no entry or an outdated one on the topic of interest) or to refer to books that are generally about the subject under consideration. The time necessary for the user to obtain an overview at the appropriate level may be large because of the volume of repetitive material obtained. Programs are needed that are able to scan hits with the particular query in mind and produce abstracts, summaries, translations or analyses of the retrieved material.