1. Introduction

1.2. Logical operators and truncation operators

Logical operators and truncation and proximity operators

Keywords can be combined by using logical operators, for increasing or reducing the number of results. 

The most common ones are:

  1. Boolean operators AND, OR, NOT (which must be written in upper case)
  2. Truncation and proximity operators
Boolean operators

Operator

Example

AND

 

Conjunction operator

It is generally implicit and  set by default even when there is no operator between the terms  

 

 

xylella AND fastidiosa

or

xylella fastidiosa

 

The result includes both the terms

OR

Inclusion operator

Useful for retrieving  synonims 

xylella OR Xanthomonadaceae

 


 The result contains one or the other term 

NOT

Negation operator

It excludes from search the second term

xylella NOT fastidiosa

The result includes only the first term


Truncation and proximity operators

(*) asterisk

at the end of a word allows you to search different words with the same rooth and different ending

Es.: environment* finds both environment  and environmental

(?) wildcard

inside a word allows you to substitute one or more letters: 

Es.: behavi?r   finds behavior and behaviour

 (“ “) quotation marks

allow you to find adjacent terms in a phrase: 

Es. : “xylella fastidiosa”  finds all the documents where xylella and fastidiosa are close in the text 

Warning: be careful with NOT operator; use it only when it is actually necessary to narrow the list of results, for example to disambiguate a keyword, in order not to exclude relevant results from your search.