3.6.1 Search tools

Boolean and proximity operators

In the context of database searching, Boolean logic refers to the logical relationships among search terms. Classical Boolean operators are ‘AND’, ‘OR’ and ‘NOT’, which can be used in most databases. Importantly, in some databases, such as PubMed, these Booleans need to be entered in uppercase letters. Other operators, the so-called proximity operators, are ‘NEAR’, ‘NEXT’ and ‘ADJ’. A more detailed overview of Boolean and proximity operators is provided in Appendix.

Truncation & wildcards

Truncation can be used when all terms that begin with a given text string are to be found. Different databases use different characters for truncation with different functionalities. For example, in PubMed, OVID and EMBASE ‘unlimited’ truncation is represented by the asterix ‘*’, but OVID Medline also uses ‘$’.

In OVID Medline the ‘optional’ wildcard character ‘?’ can be used within or at the end of a search term to substitute for 1 or 0 characters. In contrast, in EMBASE a question mark indicates exactly one character.

A more detailed overview is provided in appendix.