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Research on the nature of knowledge-based systems for bibliographic information retrieval is summarized. Knowledge-based search tactics are then considered in terms of their role in the functioning of a semantically based search system for bibliographic information retrieval, EP-X. This system uses such tactics to actively assist users in defining or refining their topics of interest. It does so by applying these tactics to a knowledge base describing topics in a particular domain and to a database describing the contents of individual documents in terms of these topics. This paper, then, focuses on the two central concepts behind EP-X: semantically based search and knowledge-based search tactics.

A self-administered questionnaire was completed by 145 Directory Assistance operators who used video display terminals (VDTs) to retrieve listings and by 105 control subjects who performed identical work except that they retrieved listings from printed paper records. The two groups exhibited few differences in their experience of work-related physical discomfort, in job satisfaction, or in their concerns about job security. Both groups were found to use eyeglasses and contact lenses to the same extent. VDT operators generally did not obtain special corrective lenses for work. The results show that replacing paper documents with VDTs need not adversely affect the comfort and morale of office workers.

Telephone operators served as their own controls in two field studies of advanced furniture designed for video display terminal (VDT) workstations. The advanced furniture was characterized by dimensions that were easily adjusted by users, in contrast with conventional furniture that provided either no adjustments or inconvenient adjustments that could only be made with difficulty. An eight-week study focused on advanced VDT tables, and a fiveweek study focused on advanced chairs. Four combinations of advanced and conventional workstation components were compared. Although on-the-job discomfort was reduced when either conventional component was replaced with an advanced component, the effect was far greater when the advanced table and the advanced chair were used together. The adjustments of the advanced furniture were reported to be easy to use, and the advanced furniture was rated more highly than the conventional furniture.

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Knowledge-based search tactics are discussed in terms of their role in the functioning of a semantically-based search system for bibliographic information retrieval. This prototype system, EP-X, actively assists users in defining or refining their topics of interest. It does so by applying search tactics, to a knowledge-base describing topics in a particular domain and a database describing the contents of individual documents. arises because: 1. The searcher needs to learn more about the topic area; 2. The searcher is having difficulty expressing her interest clearly; 3. The searcher needs to broaden or narrow her topic because too many or too few documents have been retrieved. Over the past five years, we have been studying ways to assist such information seekers and Krawczak, 1989). This paper summarizes our results and current conclusions about the design of computerized search intermediary systems. Particular attention is given to the idea that, in a semantically-based search system, knowledge-based search tactics can be applied to help the searcher explore a topic area. DEVELOPMENT OF A SEMANTICALLY-BASED SEARCH SYSTEM As part of the initial development of EP-X, we studied intermediaries who were also experienced indexers at Chemical Abstracts Service. Thus, in addition to having experience as intermediaries, they were very knowledgeable about a particular field of chemistry and about the practices and policies followed at Chemical Abstracts when indexing documents in that field. Based on several informal studies of these intermediaries, we concluded that there were four critical aspects of the interactions that we had observed: language fact retrieval, ACM Transactions on Database Systems.M.H. EP-X: A knowledge-based system to aid in searches of the environmental pollution literature.

Knowledge-based search tactics are discussed in terms of their role in the functioning of a semantically-based search system for bibliographic information retrieval. This prototype system, EP-X, actively assists users in defining or refining their topics of interest. It does so by applying search tactics to a knowledge-base describing topics in a particular domain and a database describing the contents of individual documents. This paper reviews the empirical studies that lead to the two central concepts implemented in EP-X: Semantically-based search; Knowledge-based search tactics.

A prototype Prolog system has been developed for online bibliographic retrieval. Most online bibliographic retrieval systems may be characterized by queries based on the occurrence of keywords and by databases consisting of possibly millions of records. Such systems have very fast response times but generally lack any deductive reasoning capability.An expert system for online bibliographic retrieval, developed in Prolog, would provide enhanced retrieval capabilities through the application of deductive reasoning. Such a system would permit knowledge-type queries to be asked in addition to the traditional keywordtype of queries.A concern with using Prolog to perform an online search of a million-record data base is that the response time would be unacceptable. In order to overcome this drawback two alternatives are examined: a special-purpose hardware device and an extended Prolog capability.