抄録
The indexing policy for the MEDLARS system is well organized and administered. It has also been believed that good searches can only be attained by observing the indexing rules. However, the MEDLARS indexing rules are too complicated for indexers to remember completely, and certain decisions are left to their discretion. In actual practice, therefore, good searches are not always guaranteed by simply following the indexing rules. In fact, we find it very difficult to have search concepts agree exactly with indexing concepts, and in this sense, even MeSH can only be used as a guideline. For example, the common practice of solely using the linkage of the MeSH Main Heading and Subheading in searching sometimes results in missing many relevant citations. Fortunately, in online searching in DIALOG, any fragment term or word from the indexing and any single word from the title or abstract can be searched. Therefore, with the knowledge of the indexing rules, better search strategies can be formulated using the free-text capabilities. This then becomes the task of the information-search specialist. He must attempt all of the possibilities that online searching presents in order to minimize the omission of relevant Information.