Boolean logic
As well as thinking about the search terms to use to describe
your subject, you also need to think about how they relate to each
other. Some databases use Boolean
logic to link search words together. This system uses
words such as AND, OR, NOT to
demonstrate the relationship between your search words as the
following examples show.
AND - Combining two different subjects together
You will probably want to link at least two subjects together.
This is probably the most frequent type of search performed. The
diagram below shows an example of a search for items about
spectators and soccer . It will only retrieve
those records which contain both the search words as represented by
the blue shaded area below:
This type of search is often known as an 'AND' search
ie: spectators AND soccer.
The more words that you link together in this way the more
specific the search is. Since the results will have to contain all
your search words, they should be more relevant but fewer results
will be found.
In this type of (Boolean) search you would usually need to use
the word AND to link the words: eg: spectators AND
soccer (as in the Ebsco databases) . Other databases (such
as the FirstSearch databases) will automatically perform an 'AND'
search including all the search terms you enter if you just leave a
space between each word.
OR - Including alternative words in a search
Sometimes there are several words that could be used as
alternatives to each other in a search and you need to find just
one of them in a resource for it to be relevant. For example, you
might want to search for any of the terms anorexia, bulimia
or eating disorders . You would not need all three words
to be found in a record: any one of them would be relevant for your
search topic. Records could be retrieved from any of the three
shaded areas below:
This type of search is known as an 'OR' search ie:
anorexia or bulimia or eating disorders
The more words that you link together as alternative words, the
less specific the search is. More results will be found, but these
may be of low relevance. The word 'OR' in Boolean logic is used as
a link word to find any records which contain one of the words, or
both /all of them.
This type of search is usually used in combination with an 'AND'
search. For a search on women's soccer, the resulting search could
then be expressed as shown below:
soccer AND (woman OR female)
soccer AND (wom*n OR female)
If two ideas are combined as above and there are possible
alternatives available, then the alternative terms must be enclosed
in brackets as shown. If they are not, then in the example above,
all records containing the word female will be retrieved,
regardless of whether female is linked to soccer. The second of the
examples above shows how alternative spellings can be used to pick
up records containing both woman and women (see under Step two
above).
NOT - Excluding words from a search
Sometimes you might want to remove a word from your search to
prevent resources that include that word from being retrieved. This
type of search has to be used with care so that relevant records
are not excluded. For example, you might want to search for
articles about counselling but exclude records from the publication
Dissertation abstracts international which we can't supply on
inter-library loan. The shaded area below shows which records would
be retrieved:
This type of search is known as a 'NOT' search ie:
Counseling NOT Dissertation abstracts international
Excluding words from a search makes the search more specific.
Therefore there will be fewer results, but these should be more
relevant. The word 'NOT' in Boolean logic is used in front of the
word which you want to exclude. The search tool will then find any
resources that contain the first word, but NOT the second, such as
York NOT new. The search would then retrieve
records about York in England but NOT New York.
Go to Step Four