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Boolean Searching
Database searching is based on the principles of Boolean logic. Boolean
logic refers to the logical relationship among search terms and is named
for the British-born Irish mathematician George Boole.
Boolean logic is
essentially very simple. When used in constructing a search expression, it
can be very useful in specifying exactly what information you want.
The basis of Boolean logic can be illustrated by the following diagrams:
Boolean 'AND'
This is expressed as 'blue AND yellow' in a search.
When using AND
in this search expression, results retrieved will contain both blue and
yellow information. The results will not include those documents
containing only blue or only yellow information. In the diagram the
documents retrieved by using this search expression are contained within
the green area.
EXAMPLE:
art AND schools
This will retrieve all records containing both keywords art and
schools.
Boolean 'OR'
This is expressed as 'blue OR yellow' in a search.
When using OR
in this search expression, results retrieved will contain either blue
information, or yellow information, or blue and yellow information
together. Such a search will not merely retrieve documents containing only
blue information or only yellow information. In the diagram the documents
retrieved by using this search expression are contained within all the
colour areas.
EXAMPLE:
ceramics OR pottery
This will retrieve all records containing the keywords ceramics or
pottery, as well as those containing both.
Boolean 'NOT'
This is expressed as 'blue NOT yellow' in a search.
When using NOT
in this search expression, results will contain only blue. The NOT
operator will exclude yellow completely and thus any green information
will be excluded also. It is important, therefore, to be careful when
using this operator in order to avoid hindering your search. In this
diagram the documents retrieved by using this search expression are
contained within the blue area.
EXAMPLE:
film NOT photography
This will retrieve all records containing the keyword film but not
the keyword photography.
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