When using parentheses make sure opening and closing parentheses are in the appropriate places to ensure proper execution. Parentheses give you a lot of control over your search syntax. Finally, of the remaining records, any records that contain the search term asthma will be excluded from the results returned. Of those records, only records containing lung cancer will be retained. The above search will first consider the inner set of parentheses, COPD OR lung disease, finding records that contain both the search term and search phrase, or just one of them. (“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. The above example would exclude any record mentioning asthma, no matter whether a record talked about the research being relevant to asthma or not relevant to asthma.Ĭompound Boolean Search Syntax and the Power of Parentheses NOT needs to be used with caution as it does not take account of context. The above search will return records containing either COPD or lung disease while excluding records containing the search term 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. Not all terms or phrases have to occur in the records returned. The above search will return records where at least one of the search terms or phrases occurs in the records returned. 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. The above search requires that the records returned contain both the search term and search phrase.Ĭonversely, OR is best used when you want to do a broad search about related topics. 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.ĪND is best used to narrow search results by requiring all of the search terms or phrases in the query (or part of a query) to occur in each record returned. 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 relationships among multiple search terms and phrases.
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