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Boolean Operators

Using What You've Found to Find More

From Portland State University
Text-/image-based version of this info 

Searching Databases

Overview of database search tips.
From Yavapai College Library. 

More Resources

Why use Boolean operators?

Most library databases use Boolean operators (ANDOR, and NOT). 

Use them to narrow or broaden search results.

  • AND for records that include both terms (narrows search)
  • OR for records that include either term (broadens search)
  • NOT to exclude irrelevant concepts (narrows search)

Example: Iran AND China AND (energy OR petroleum OR oil) 

Adapted from SAIS Library, Johns Hopkins Univ. "Database Search Tips" Guide (no longer extant).

Boolean Operators

Use AND, OR, and NOT to narrow or broaden search results.

Using AND

  • narrows results
  • ALL terms must be in each search result

Note: in most, but not all, databases, the AND is implied. For example, Google automatically puts an AND in between search terms.

Example:  renewable energy AND China

Using OR

  • broadens results
  • searches for ANY of the terms in search results
  • connect similar concepts (synonyms)


Example:  renewable energy OR solar OR wind


Using NOT

  • narrows results
  • exclude words from search

Example:  peacekeeping NOT United Nations


Adapted from SAIS Library, Johns Hopkins Univ. "Database Search Tips" Guide (no longer extant).

Too Few Results?

Don't give up! Reassess your search strategy.

Possible Reasons:

1. Choice of Search terms
Choosing the right search terms is key.

  • Experiment with related terms.
  • In databases Subject Terms can help you identify keywords.
  • Use OR to search for multiple related terms simultaneously. (e.g., policy OR law)

2. Too Many Search Terms
Database can be picky about search terms. Be selective.

  • Begin with one of two search terms that best represent your topic. Then add other terms as needed.
  • Avoid long phrases and empty words like “the” and “how.”

3. Too Many Limiters
If you limited the search (e.g., by date or search field) remove limiters and reassess.

4. Narrow Topic
Highly specific topics may be too narrow for finding results. Try a broader related topic first. 


  • Narrow search: Bloomington Indiana AND environmental policy
  • Broader search: United States AND state government AND environmental policy

5. Database Choice
Different databases focus on different topics. View Resources by Subject or Ask a Librarian.

Too Many Results?

1. Add additional keywords.

  • TIP: In databases Subject Terms can help you identify more narrow topics and keywords.

2. Choose more narrow search terms.


  • Broader term: law
  • Narrower term: "environmental law"

3. Use limiters. (e.g., search fields like title or abstract, publication date, format type).

   In OneSearch see options under Refine Search.

4. Search for a short phrase with quotation marks. 


  • "environmental law"
  • "environmental justice"

Database Search Fields

Records in library databases are made of "fields." Fields can help narrow your search.


  • author
  • title
  • journal title
  • abstract
  • publisher
  • date/year of publication
  • subject/descriptor
  • all text (searches the full text, if available)


Improving Search Results with Fields

  • Most databases automatically search by keyword (looking for the term anywhere in the record).
  • Limit the field for a search term to narrow the results. 
  • Fields are usually in drop down boxes.
  • If the database has a single search box with no drop-down menu, look for an "Advanced Search" option.

Adapted from SAIS Library, Johns Hopkins Univ. "Database Search Tips" Guide (no longer extant).

Subject Terms

Subject Terms can help you identify effective keywords. Most databases list Subjects in their search results.

For example, in OneSearch

1. Do an initial search. 

2. Under Refine Search click on Subject.

Phrase searching

Use quotation marks or parentheses around search words to search for a phrase. (Otherwise most databases will find records that include both terms, but not necessary the terms as a phrase.)


"middle east"
"united nations peacekeeping forces"
"civil society"

Adapted from SAIS Library, Johns Hopkins Univ. "Database Search Tips" Guide


Truncation broadens your search to include variant word endings and spellings. Enter the root of a word and then the truncation symbol.


elect* = election, electoral, elections
econ* = economy, economic, economics, econometric, economique
politi* = politics, political, politician, politique, politische

The most commonly used truncation symbol is an asterisk (*)
A exception is LexisNexis Academic, which uses an exclamation mark (!).


Adapted from SAIS Library, Johns Hopkins Univ. "Database Search Tips" Guide


Nesting is the use of parenthesis to put search words into sets. Use nesting with AND, OR, or NOT, 

success AND (education OR employment) 

(records will contain the word success, AND either the word education OR the word employment)

Nesting is often used when search terms have similar meanings:

education AND (employment OR jobs)


? Wildcards are similar to truncation, but substitute a symbol for just one character.


wom?n = woman, women

democrati?ation = democratisation, democratization

defen?e = defence, defense

19?? = any  number between 1900 and 1999

The most commonly used single wildcard symbol is a question mark. Some exceptions:

  • LexisNexis Academic uses an asterisk (*). 
  • Some databases uses the pound (#) symbol. 

If in doubt, check the help screens of the database you're using.

Adapted from SAIS Library, Johns Hopkins Univ. "Database Search Tips" Guide