When would you use keyword searching?
1. There is no subject heading for your topic.
(ex: topic / concept is very current or very jargon-oriented)
2. Subject headings are too broad.
3. You want to combine several keywords.
Boolean Operators
Boolean searching is based on a system developed by George Boole, a 19th century mathematician. Most library databases support Boolean searching and most Internet search engines support Boolean searching through their advanced search option. The power of Boolean searching is based on connecting keywords with boolean operators. The three basic operators are AND, OR and NOT. Here is how they work:
AND
Type AND between your keywords to narrow your search. The database or search engine will only retrieve those articles or web pages that contain both words. Using AND will decrease the number or hits or articles or web pages in your result list.
Example: school AND crime
Note: Some search engines allow you to type a plus sign (+) in front of a keyword when doing a basic search. This works the same as AND.
Example: +school +crimeOR
Type OR between your keywords to broaden your search. The database or search engine will retrieve those articles or web pages that contain at least one of these words. Using OR will increase the number of articles or web pages in your result list (especially if not used in combination with AND or NOT). Use OR between keywords that are synonyms or have similar meanings.
Example: baby OR infant
NOT
Type NOT before a keyword to exclude that keyword from your search. Using NOT will also narrow your search. Using NOT will decrease the number of articles or web pages in your result list. Be careful when deciding whether you should use NOT in your search. The best use of NOT is when you are searching for a keyword that may have multiple meanings.
Example: saturn NOT car
Note: Some search engines allow you to type a minus sign (-) in front of a keyword when doing a basic search. This works the same as NOT.
Example: +saturn -car
Keyword Vs. Subject Searching
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Keyword Searching |
Subject Searching |
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Any significant words / terms describing your topic can be considered keywords. Good search to start out with if you do not know the subject heading used for your topic. |
Pre-defined "controlled vocabulary" words used to describe the content of each item (book, journal article) in a database. Search terms must come from the database's thesaurus. |
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Searches for keywords in any number of fields (ex: title, author, summary, subject, and/or the full text of documents). |
Searches for subject words only in the |
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More flexible search. Can combine keywords in various ways (Boolean searching). |
Less flexible search. Need to know the exact controlled vocabulary term. |
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May yield too many or too few results depending on keywords used. |
Number of items retrieved potentially smaller. If too many results, may use subheadings to focus on one aspect of the broader subject (ex: InfoTrac OneFile). |
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May retrieve irrelevant items. |
High degree of relevancy. |
How to Use Boolean Operators