عنوان مقاله [English]
In online catalogs, searching based on subject keywords, comprise a significant percentage of searches. Various studies, especially those of US origin, have stated it to be more than 50 percent. Due to the importance of subject searching in online cataloging systems for users, much efforts is being exerted on the part of researchers and designers of such cataloging systems to increase its performance and ease of subject searches. The present study offers a brief overview of subject searching and then deals with the knowledge necessary for carrying out a subject search. It further deals with the issues facing users when doing subject searching, optimization of catalog structure, and Z39.50 information retrieval standard.