The Boolean Operators
AND
OR
NOT
are the most frequently used boolean operators. The AND, OR, and NOT are used to combine search statements (i.e., search sets) together. By combining search statements, you are creating relationships between concepts in order to best represent the topic for which you are searching.
OR
OR is used to link synonyms. By combining two or more search statements using OR, a set will be created which contains all the documents containing any of the query terms (with duplicates eliminated).
Examples:
any of the three trimesters of pregnancyIf you are searching for spontaneous or induced abortions, you would first search for "spontaneous abortions," then you would search for "induced abortions." Your retrieval would look something like this:
The next step is to create the relationships between the two subjects using the Boolean OR.
First, click on the "Combine" icon, then select the sets you wish to combine. Be sure that the OR operator is hilited, and click on the "continue" key:
Your results will look like this:
Another method for combining sets is to bypass the menu options and enter the commands directly on the "Enter Search" line. This is called "direct entry." When using direct entry, combine using the set numbers, like this:
AND
AND is used to to find the union of two or more sets. By combining two or more search statements using AND, a set will be created which contains only those documents which contain each and every query term.Examples:
hiv infections in laosIf you are searching for cocaine-related heart diseases, you would first search for "cocaine," then you would search for "heart diseases." Your retrieval would look something like this:
The next step is to create the relationships between the two subjects using the Boolean AND.
First, click on the "Combine" icon, then select the sets you wish to combine. Be sure that the AND operator is hilited, and click on the "continue" key:
Your results will look like this:
Another method for combining sets is to bypass the menu options and enter the commands directly on the "Enter Search" line. This is called "direct entry." When using direct entry, combine using the set numbers, like this:
NOT
By combining two search statements using NOT, a set will be created that contains those documents with the first query term, but which specifically excludes those documents with the second query term.Example:
health care reform NOT health maintenance organizationsUsing this example, you would first search for "health care reform" then for "health maintenance organizations". The next step is to create the relationships between the two subjects using the Boolean NOT.
The NOT operator is not available as a "combine sets" option. Instead, you must bypass the menu options and enter the commands directly on the "Enter Search" line. This is called "direct entry." When using direct entry, combine using the set numbers, like this:
ADJ and ADJn
The ADJ and ADJn operators are used in text word (title and abstract word) searching. They can be entered via the "direct entry" method, whereby you type two or more query words directly on the "Enter Search" line. When two or more query words are separated by spaces on the Command Line, Ovid assumes them to be adjacent, and automatically inserts the adjacency operator ADJ between the words before processing the query. The query terms will be found in the specified order.Example:
If you type:If you wish, you may separate query terms by manually inserting ADJ between them, but this is not necessary. For example, the search "blood pressure" is identical to the search "blood adj pressure."
The defined adjacency operator ADJn retrieves two or more query terms within n words of each other, and in any order. The number n may be any number 1 through 99, and should immediately follow ADJ without a space, e.g., "ADJ7, ADJ3," etc.
For example, the search "physician ADJ5 relationship" will find the words "physician" and "relationship" within 5 words of each other. This would retrieve documents with phrases such as "physician patient relationship," "patient physician relationship," "relationship of the physician to the patient," etc:
ADJn is ideal for those queries in which you are not exactly sure of the phraseology that may have been used in the literature. Also, requiring two or more query terms to be near each other will usually retrieve documents in which the query terms are closely related.
FREQ
The frequency operator FREQis used in text word (title and abstract word) searching. It can be entered via the "direct entry" method, whereby you type two or more query words directly on the "Enter Search" line. FREQ allows you to specify a threshold of occurrence for a term.
This operator is particularly useful when you are searching the full text (TX) field for a somewhat common word or phrase. The Frequency Operator will ensure that your query word or phrase will be retrieved only if it occurs at least the number of times that you specify. In general, documents that contain many instances of your query term will be more relevant to you than documents that contain few instances of your query term.
Syntax for this operator is as follows:_______
x.fd./freq=n
x is the query, fd is the 2-letter
field name, and n is the threshold frequency.
Example:
If you searchThe frequency operator can not be used in search commands with multiple fields, or with fields that consist of a combination of other fields (e.g., the TW field.) Use this link for an explanation and list of field labels.
For example, the
following searches are not permitted and will result in error messages:
If you type:_______science.ti,ab./freq=3
The system won't accept it because you have searched for more than one field, the title (.ti.) and the abstract (.ab.) fields.
Instead, to make the request acceptable to the system, you would have to type:
_______blood.ab./freq=5 or blood.ti./freq=5
