Keyword search should be preferred if
- you have a very specific subject and there are no suitable subject terms;
- terminology of the field is too new and has not yet been included in the subject heading list;
- terms in the thesaurus are too general;
- the subject includes signs, symbols or numbers;
- there is no subject index (Internet search engines do not contain subject indexes).
Subject search should be preferred if
- the subject is well provided with subject headings;
- the subject is very general;
- homonyms (similar words with different meanings) can be used to describe the subject;
- you do not wish to find out all synonyms important for key word search;
- the precise meaning of search words is important.
It cannot be said that one search strategy is better than the other. Both of them can have their advantages, and they can be combined to obtain the best results.
Build search using the key words of your own choice and examine the subject headings of relevant documents. You can continue your search by clicking on suitable subject headings, or add words from the subject index into your query, or rephrase it and perform a new search.
Another way is to start your search with a subject heading and specify the search with the subject headings found in retrieved documents.