Citations for books and articles provide basic information such as the author of the work, its title, publication information and so on. Each of these types of information is called a field and can be used to search a particular part of the record. For example, when you use an author search you are searching only the author field. Keyword searches give you the option of searching all the fields at the same time but that may produce an unmanageable number of irrelevant hits. Subject searching with controlled vocabulary produces fewer but more relevant hits.