CINAHL® subject headings terms are arranged in a hierarchy, or "tree structure", that permits searching at various levels of detail from the most general level to more narrow levels to find the most precise terms. The subject headings include indexing annotations, scope notes, entry vocabulary , history notes, and allowable subheadings. The subject headings can be exploded to retrieve all references indexed to that term as well as all references indexed to any narrower term(s). Searches can also be limited with specific qualifiers (subheadings) to improve the precision of the search, and limited to major subject headings, which indicate the main focus of an article.
