If you do not use boolean operators to connect your search terms, databases may be set up to make assumptions about your search statement.

For instance, when you enter search terms without using a connector, such as:
 

be aware that the database may be set up to do one of three things. 
 

	Search for records containing all three terms
	ozone layer depletion ozone and layer and depletion
	This is called "implied AND"  Many database searches use this as their default. This is likely to retrieve many irrelevant records as well as relevant.

	Search for items containing any of the terms
	ozone layer depletion ozone or layer or depletion
	This is called "implied OR" and is often employed by Web search engines.  This may retrieve thousands of irrelevant records.

	Search for a phrase (i.e. 2 or more adjacent words that occur in an exact order)
	ozone layer depletion "ozone layer depletion"
	This is called "phrase searching" and is rarely the default with search engines.