Boolean
operators are words and/or
symbols (depending on the database) that are used in combination
with search words and/or phrases to:
Reduce (narrow, make more
Precise)
the number of records resulting from a database search.
Expand (make more
comprehensive, increase Recall)
the number of records resulting from a database
search.
The usual
Boolean
operators are
"and"
"or"
"not"
They are derived from a field of
mathematics called "set
theory," which is
concerned with the characteristics of any group of items that make
them a "set"
Example 1:
All the CDs that the band
Nirvana was on is a "set."
All the compilation CDs
that the band Nirvana was on with other bands is a
"set."
The set of all CDs that
only Nirvana on is a "set."
The last 2
sets
together form the first set.
Example 2:
The
"set"
of all fruit includes oranges, kiwi, apples, star fruit, all
melons, grapefruit, bananas, and many more.
Example 3:
All books in the library by
Toni Morrison are a "set."
General purpose of
Booleans:
Targeting the search.
This means to narrow the
results of your search to just the records that are relevant
(Precision).
Making the search comprehensive.
This means to expand your
search to ensure that you get all the possible records that are
relevant (Recall).