For example: (“lung cancer” AND (COPD OR “lung disease”)) NOT asthma Likewise, nested parentheses are considered from the inside out. Just like in math, the terms or phrases contained inside of parentheses are considered together. You can control the order your search terms and phrases are searched by using parentheses to group search terms and phrases. Compound Boolean Search Syntax and the Power of Parentheses The above search will return records containing either COPD or lung disease while excluding records containing the search term asthma. For example: (COPD OR “lung disease”) NOT asthma The NOT operator can be implemented in one of two ways, either by using the boolean operator NOT or by using the minus sign ( - ) directly in front of the term or phrase to be excluded. NOT is best used when searching for a topic that often co-occurs with another topic that you wish to exclude. For more information see the Relevance section. Not all terms or phrases have to occur in the records returned, however, results are sorted by relevance, meaning records that contain a higher number of the search terms or phrases, or have a higher quality match for the fields searched, will be returned higher in the results list. The above search will return records where at least one of the search terms or phrases occurs in the records returned. For example: “lung disease" OR COPD OR “lung cancer” Use the OR operator when it is not necessary for all terms or phrases to occur in each of the resulting records. Each of the results returned will include one, several, or all of the search terms or phrases included in the query. ORĬonversely, OR is best used when you want to do a broad search about related topics. The above search requires that the records returned contain both the search term and search phrase. ANDĪND is best used to narrow search results by requiring all of the search terms or phrases in the query to occur in each record returned. It is important to understand when to use each boolean operator and how to construct compound boolean syntax to get the most out of your search. Boolean search logic is executed by using the operators AND, OR, or NOT between each search term or phrase. Boolean operators help define the logical relationship among multiple search terms and phrases.
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