Boolean operators allow you to combine your keywords into search queries.
The words AND and OR are the most commonly used Boolean operators. Another is NOT, which is difficult to use because it can exclude useful results.
AND combines your search terms and looks for them together in search results. For example, a search for 'mind AND spirit' will retrieve records that contain both search words.
OR separates your search terms, finding records that contain either keyword. For example, a search for 'mind OR spirit' will retrieve records that contain just one of the search terms as well as records with both of the search terms.
NOT finds records that only have the first keyword, excluding the second keyword. For example, a search for 'mind NOT spirit' will only find recrods containing mind but not the second keyword. However, if there was an article entitled Mind as it Relates to the Spirit, the database will ignore the article even though it is useful because of the use of the Boolean Operator NOT.
Authority
Scope, Coverage & Relevance
Bias & Accuracy
Currency / Timeliness
Quality