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Searching Solutions: Keywords vs Indexed

Understanding how searching changes from search engine to database.

Keywords vs Indexed

In developing searching strategies, keywords are the terms that are used in an article or abstract. Many times, keywords will be all you need. However, if you don't guess the term the author used for your topic, you will not find that article.

In indexed databases, no matter what term(s) an author uses (or neglects to use), there will be one subject heading applied for that topic. In the following example, you would have to search with every keyword term in order to find all the articles on cat scans. However, in PubMed, you only need to use one subject term to collect all indexed articles on cat scans.


  • Keywords: cat scan / ct scan / x-ray scan / tomography / tomodensitometry / ct x ray / cine ct
  • PubMed MeSH (thesaurus/subject) Term: Tomography, X-Ray Computed



  • Author selected
  • Word in title or abstract (or other text field in a database)
  • For full-text databases: any word anywhere in an article (often including footnotes and references)

When selecting keywords, consider all the different options an author might use for that concept, then link them together using the Boolean OR term. AND together different concepts.

The USC Libraries' Developing Keywords tutorial can help you practice identifying potential keywords to search a database.

Always use keywords to search Non-Indexed databases.

Keywords to Subject Term

Different databases use different subject terms for author keywords. When searching for terms related to heart attacks in PsycINFO, use the terms Heart Disorders.

Keywords to Subject Term


Indexed / Thesaurus / Controlled vocabulary

  • Word(s) and/or phrase(s) used to describe a specific concept or idea
  • Individual citations are reviewed, usually by a subject specialist, and the appropriate term is applied (even if the author dies not use that exact term)
  • In some databases, the subjects (or disciplines) may (or may also) be applied to the journal from which the citation came (e.g., Scopus)
  • Indexed databases generally provide a link to their thesaurus:

When searching with the controlled vocabulary, choose the broadest term (higher on the hierarchy) that applies to your topic. You may also want to OR a related keyword. AND together different subjects for your search.

For more details, visit: Indexed Databases.

PubMed MeSH Hierarchy Tree
MeSH hierarchy tree

Example: (Climate processes [mesh] OR "climate change") AND california

Tips to Remember

  • Each database may have its own indexing terms
  • Not all databases use indexing (e.g. Google Scholar and Web of Science)
  • You can use the Advanced search to discover available terms and search options
  • Databases or search engines that pull from multiple sources (e.g. USC Libraries and ProQuest) may also pull the indexing terms from the underlying databases (e.g. PyscINFO and MEDLINE)
  • Indexing terms are not always how people talk (Latino vs. Hispanic) and may be unique to that database
  • It takes time to add indexing terms to citations; searching only for indexed terms will not retrieve the newest citations
  • Your final search will generally combine both indexed terms (e.g. MeSH, Subject Terms) and other (key) words