What is the difference ?
Both have inherent advantages and disadvantages, and therefore when conducting a comprehensive literature search, both techniques are generally employed.
Subject heading searching is done in databases that have a formal thesaurus. The thesaurus is basically a controlled vocabulary of approved subject terms that describe the content of the articles included in that particular database.
Subject headings are referred to differently in different databases. In MEDLINE, they are referred to as MeSH Headings (Medical Subject Headings). In CINAHL, they are referred to as CINAHL headings. In other databases they are referred to as descriptors, and in others, they may be referred to simply as "subjects".
Subject headings are tremendously useful to the searcher because they bring together under one umbrella term all the synonyms, singular/plural pairs, and spelling variants of a given term. This relieves the searcher of having to search on every variation of the term in order to bring up all the relevant article together. (saves time)
Not only do they bring together all variants of a word, subject headings also allow retrieval of more relevant articles.
Go to CINAHL
Search for keyword "aids" - 33206 entries
Search for Subject Heading "aids" - Use Advanced Search and click on Suggest Subject Term
AIDS Use: Acquired Immunodeficiency Syndrome 11153
Click on box beside Acquired Immunodeficiency Syndrome and then go to extreme right and click on Search Database
Can do this in both CINAHL and Medline
Explode allows you to take terms from the thesaurus and include all the narrower terms into your search.
Eg. search for heart failure