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Boolean Searching

Table of Contents

Introduction | Tips for Successful Boolean Searching

Introduction

Boolean searching is among the most powerful ways of searching a computer database. You may perform this type of search in Web databases or any of the library's CD-ROM indexes. Boolean searching is not difficult, but it does require that you think carefully about exactly what information you are seeking from the computer and develop your search strategy accordingly.

When you perform a Boolean search, you search the computer for the keywords that best describe your topic. The unique power of Boolean searching is that you combine these keywords using three "operators." Which operator you choose to combine your keywords determines how the computer performs the search and what information it returns to you. These operators are the three words:

and or not

and * Use this when you want to focus or narrow your search *

The operator and tells the computer to search its database for every entry or record that has both of the words somewhere in the same entry or record. For example, if we want to find information on "Kansas basketball," we might search the appropriate computer in this way:

basketball and kansas

The Venn diagram above illustrates what happens. The computer goes through its database and retrieves every record it finds with the word "basketball" and every record with the word "kansas." It then gives us only the shaded area where the circles intersect. That is, those records in which both words appear somewhere in the same record.

or * Use this when you want to broaden your search *

When we combine our keywords using the operator or we tell the computer to retrieve every record that has at least one of those words in it. Both do not have to appear. If either word is present, the computer presents us with the record. For example, if we wanted to find all the information the computer has on either "bosnia" or "serbia," we might try this search:

bosnia or serbia

As the diagram above shows, the computer again goes through its database and finds every record with the word "bosnia" and every record with the word "serbia." It then presents us with every record it found, every record with at least one of the words we specified in our search. Using the "or" operator will usually result in the retrieval of a great many records.

not* Use this when you want to do a more specific search *

The final operator is not. Combining our search terms with this operator allows us to strip a term out of our search, telling the computer we want to see everything it has with the first word but nothing that mentions the second word. For example, if we're looking for material on the "Jurassic era," we might want to remove any mention of the best selling book by Michael Crichton (such as book/movie reviews). We might try this search:

jurassic not park

Once more, the computer goes through its database and extracts every record with the word "jurassic." Of that group of records the computer will display only those in which the word "park" does not appear, as the diagram above illustrates. We will not see any record that has both words.

Tips for Successful Boolean Searching

1. Using the operators and and not will always narrow your search, increasing your specificity and decreasing the number of "hits", or records retrieved by the computer. The operator or broadens your search, increasing the number of hits.

2. Before you sit down at a computer to perform this type of search, you should have thought carefully about what words you want to search. The librarians strongly recommend that you develop a vocabulary that contains words describing your topic. This should include synonyms for all your key concepts. If the computer finds nothing using one word, try doing the same search again but substitute a synonymous term. You may get quite a different result from the machine.

3. In addition to having your vocabulary prepared, you should already have decided how you want to combine your keywords, i.e. which operators you want to use with which words. Computers are very literal-minded and very unforgiving. If you don't know what you want to look for and how you want to look for it, the computer will probably be of little use. You could easily spend a great deal of time searching around and find nothing.

4. You may use more than one operator in a single search.

automobiles and accidents and kansas

* This search would look for records that have all three words.

automobiles or cars or vehicles

* This search would look for records that have any of the three words.

5. You may use different operators in a single search, but you must be careful when trying it. Computers usually perform and and not searches first, and then or searches. If we were looking for information on business in the states of either Kansas or Missouri, we might try this search:

kansas or missouri and business

NOTE: Searchers may get around this by wrapping the or words in a parenthesis. This is called "nesting." It forces the computer to search the parenthesized words first, before anything else. So in order to run the above search correctly, we would type in:

(kansas or missouri) and business

6. Truncation allows us to search for a root word and all of its various endings, such as plurals. The symbol used for truncation is usually either a question mark (?) or an asterisk (*). It varies from one type of software to another. For example, if we want to find information on Native American poetry in Kansas we might try this search:

indians and kansas and poe*

Replacing the end of the word "poetry" with the asterisk (or question mark in some systems) tells the computer to look for all the various endings of the root word "poe": poetry, poet, poets, poem, poems, poetical, etc.

7. You may also use a "wildcard" character to replace letters within a word. This will allow you to catch variant spellings of certain words. For example, to find the word "color" and its British equivalent:

col*r

This will tell the computer to look for both "color" and "colour."