The following concepts are common to most computer databases of bibliographic information, including the library catalog.
The phrase to remember is: "OR" gets more while "AND" gets less
The computer is looking for individual records. Whatever you search for must be contained in each record. Therefore, using the example below,
"AND" between terms narrows the search by requiring that BOTH terms appear in each record.
Asking for Holistic medicine (A) AND headaches (B) will get only those titles which have BOTH terms assigned to each record. See shaded area above.
OR" between synonymous terms in a search broadens the scope.
If the search is for marital psychotherapy(A) OR marriage counseling(B), the results will be all those titles which are about marital psychotherapy PLUS all those titles which are about marriage counseling. See shaded area above.
"NOT" between terms narrows the search by eliminating the records that contain
one of the terms.
If you want to search for violence, but not domestic violence, you would phrase the search as violence(A) NOT domestic(B). Some computers may require you to use the phrase "AND NOT" between terms.