Guide
Home >> Using Boolean Operators
What
are Boolean Operators?
Boolean
operators form the basis of mathematical sets and database
logic. When searching databases, boolean operators are used to
connect your seach words, either to narrow or broaden your set
of results. The three basic boolean operators are: AND,
OR, and NOT.
When
should I use AND in a search?
- To narrow your search, telling the database
that ALL search terms must be present in the
resulting records.
Example:
cloning AND humans AND ethics
The
red triangle in the middle of the Venn diagram below represents
the result set for this search. It is a small set using AND, the
combination of all three search words.
When
should I use OR in a search?
- To connect two or more similar
concepts (synonyms).
- To broaden your search, telling the database
that ANY of your search terms can be present in the resulting
records.
Example:
cloning OR genetics OR reproduction
All
three circles represent the result set for this search. It is
a big set because any of those words are valid using the OR operator.
When
should I use NOT in a search?
- To exclude words from your
search.
- To narrow your search, telling the database
to ignore concepts that may be implied by your search terms.
Example:
cloning NOT sheep
Why
are Boolean operators important?
-
To focus a search, particularly when
your topic contains elements of multiple subjects.
- To connect various pieces of information to find exactly what you're looking for.
Example:
second creation (title) AND wilmut and campbell (author) and
2000 (year)
What
about search order?
Databases
are very sensitive; they follow the commands you type in and return
results based on those commands. You need to be aware of the logical
order in which words are connected when using Boolean operators.
Databases
process searches in different ways. Here are some hints that work
with many databases:
Databases
usually recognize the AND operator as being the primary operator,
and will connect search words with AND together first.
If
you use a combination of AND and OR operators in a search enclose
the words to be "Ored" together in
parentheses.
Examples:
ethics AND (cloning OR reproductive techniques)
(ethic* OR moral*) AND (bioengineering OR cloning)
There
are other ways and reasons to use Boolean operators. For more
information about constructing a good search, Ask Us!
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