Subject Terms
What are Subject Terms
A important part of the research process is knowing how to find and use controlled vocabulary. Controlled vocabularies are used by databases as a way to organize knowledge for subsequent retrieval.
Subject terms, which are descriptive words assigned to an article by a database, are a common way databases use controlled vocabularies. These subject terms denote the item's subject or main themes. Articles with similar themes, or about similar subjects, will be classified together under a very specific subject heading - instead of scattered under multiple different synonyms or searches. Searching with subject terms allows researcher to focus in on all relevant research with one search term or phrase.
Be aware that searching by subject term is different than keyword searching. Here are some differences:
| Keywords | Subject Terms |
| Natural language used to describe your topic | Controlled vocabulary defined by each database to describe the content of an article |
| Great place to start searching for articles on your topic as keywords are flexible | A more advanced search method as you need to know the exact subject heading |
| Databases will default to search for keywords anywhere in the record | Database only searches for terms specifically matching in the "subject heading" field |
| May result in irrelevant articles | Results are usually very relevant to topic |
| May result in too few or too many articles | Can use subheadings to further hone in on a subtopic |
The following video nicely outlines these differences
How to Find Subject Terms
Databases commonly provide a way to search for subject headings through their thesauri. Please note that subject headings differ across every database, therefore you first must look up the exact subject term for the specific database you are using.
While the way to find and use the thesaurus to identify subject heading is fairly similar across databases, there are a few differences. As such, there are videos for our two main database platforms - EBSCOhost and ProQuest.
Tools for Extracting Essential Search Terms
A number of acronyms have been developed as tools to determine the essential search terms for a topic.
PICo (Qualitative Studies) - Population or Problem / Interest / Context (see Murdoch University Guide)
SPICE (Social Sciences) - Setting / Perspective / Intervention / Comparison / Evaluation (see Murdoch University Guide)
PEO - Population / Exposure / Outcome (see UNC Greensboro Guide)
PICO (Health Sciences) - Patient or Population / Intervention / Comparison / Outcome
Boolean Operators
What are Boolean Operators
Boolean operators are the words "AND", "OR" and "NOT". When used in library databases (typed between your keywords) they can make your search more precise.
AND narrows a search by telling the database that ALL terms used must be found in order for it to appear in your results list. Search for two or more concepts by combining them with AND.
For instance, if you want to search by global warming and climate change, you will only get results where those are both present.
Global Warming AND Climate Change
OR will expand your search results so all results must contain at least one, if not more, of your defined terms.
For instance, if you want to search by global warming or climate change, you will get results with either or both are present.
Global Warming OR Climate Change
NOT excludes terms so that your search results do not contain any of the terms that follow it. This can be useful when:
- you are interested in a very specific aspect of a topic (letting you weed out the issues that you're not planning on addressing)
- when you want to exclude a certain type of material (e.g., a conference paper, book review, etc.)
Use NOT with caution as good items can be eliminated from your results.
For instance, searching for global warming not climate change will return results on global warming, but not those dealing with climate change.
Global Warming NOT Climate Change
Additional Operators
Parentheses are used to communicate to the database the order in which it should resolve the AND, OR, & NOT statements by nesting query terms.
You can enclose search terms and their operators in parentheses to specify the order in which they are interpreted. Information within parentheses is read first, then information outside parentheses is read next.
For example, when you enter...
(carpenter bee OR honey bee) AND pollination
...the search engine retrieves results containing the word carpenter bee or the word honey bee together with the word pollination.
If there are nested parentheses, the search engine processes the innermost parenthetical expression first, then the next, and so on until the entire query has been interpreted.
Quotation marks are used around a phrase that needs to be returned in that exact order.
For instance, “global warming” will only return results that contain the exact phrase ‘global warming.’ If you do not use quotation marks around phrases, each word in the phrase will be treated separately as if you used AND between each word. For example: a search on global warming may display results that contain the words ‘global’ and ‘warming’ but not necessarily in that order. These are not needed in all cases since a lot of times databases recognize 'global warming' and other common terms and will search them together without the need or quotation marks.