Indexes and directories.

There are a host of bibliographic and catalog databases that may be included in digital libraries. These range from the more than 20 million record database of bibliographic citations in OCLC and the millions of citations in online databases for specialized literatures such as medicine (e.g., MEDLINE) and engineering (e.g., NTIS). Tertiary databases such as citation indexes and databases of directories make information seeking more effective but require specific skill and effort on the part of information seekers. Many of the thesauri for specialized literatures are available in electronic form (e.g., Medical Subject Headings, ACM Computing Reviews Classification System) and techniques for merging and filtering these languages to allow users to search across multiple databases are emerging. Although most indexes to image and sound collections currently use words from captions or titles, new pattern-matching techniques are emerging to categorize and classify multimedia objects [10]. In the past, bibliographic instruction has been provided by librarians as a supplement to "regular" courses, but widespread availability of digital libraries will require remote instruction and support related to information-seeking skills and knowledge.

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