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HELP: Boolean Searches


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Introduction to Boolean Searching

Boolean searching, based on a system of symbolic logic developed by 19th century English mathematician George Boole, is a very powerful way of searching a computer database. The Media Catalog Search and many Internet search programs support Boolean searches.

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. There are some helpful hints you should know before you start your Boolean search.

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".

AND | OR | NOT

Which operator you choose to combine your keywords determines how the computer performs the search and what information it returns to you.


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AND

This is a very specific or narrow search.

The operator AND tells the computer to search its database for every entry (or record) that contains each of the words we specify in the same record. For example, if we want to find information on the 'supreme court', we might search the appropriate computer in this way:

supreme AND court

Two overlapping circles

The Venn diagram above illustrates what happens. The computer goes through its database and retrieves every record it finds with the word 'supreme' and every record with the word 'court'. It then returns the list of records only in the shaded area where the circles intersect. That is, those records in which both words appear somewhere in the same record. You can also perform an advanced AND search if you find the database results are too broad.


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OR

This is a very broad search and may retrieve a great many records.

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 'law' or 'legal', we might try this search:

law OR legal

OR Venn diagram

As the diagram above shows, the computer again goes through its database and finds every record with the word 'law' and every record with the word 'legal'. It then presents us with every record the database found which contains at least one (not necessarily both) of the words we specified in our search.


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NOT

This is a selective search which allows us to exclude unwanted records.

Combining our search terms with the operator NOT 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 regional court system, we might want to exclude records that pertain to the supreme court . We might try this search:

court NOT supreme

NOT Venn diagram

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


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Hints for Successful Boolean Searching

* Before You Begin

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. We recommend that you develop a small 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 different results.

* Keywords

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.

* Using the operators

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.

* Using More Than One Operator

You may use more than one operator in a single search. For example:

This search would look for records that contain all three words:

judge AND court AND trial

In this search the computer would not include any record with the first three words that also mentions 'supreme':

judge AND court AND trial NOT supreme

* Order of Operations

Computers usually perform AND and NOT searches first, and then OR searches. If we were looking for information on courts in either USA or Canada, we might try this search:

court AND USA OR Canada

Because the computer processes AND searches first, we would end up with records that have the words 'court' and 'USA' in the same record as well as all records containing the word 'Canada'. That would almost certainly not give us the result we want.

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:

court AND (USA or Canada)

* Truncation

Truncation allows us to search for a root word and all of its various endings, such as plurals.

The symbol used for truncation is an asterisk (*).When you use the Media Catalog Search , the asterisk (*) replaces several characters. For example, if we want to find information on computer grapics, we might try this search:

compu* AND graph*

Replacing the end of the word 'graphics' with an asterisk (*) tells the computer to look for any endings to the root word 'graph' such as 'graphic' or 'graphical'. The same principal holds true for replacing the last part of 'computer' with an asterisk (*).

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Advanced 'AND'

Keyword searching is very powerful because it allows searchers to combine two or more subjects, or specific aspects of subjects, to find truly relevant items.

Rules to remember:

  • If you get TOO MANY 'hits,' add a term to make your search more specific.
  • If you get TOO FEW 'hits,' take away a term to make your search less restrictive.
    Alternately, experiment with different words that relate to your subject.
  • If you're finding NOTHING, try different search words.

This Venn diagram gives a visual conception of how two or more subjects can intersect, creating an area of overlap that combines multiple subjects.

Advanced AND Venn diagram

Examples:

Adolescents and Abuse and Rehabilitation

Computers and Security and Management

Pollution and Government and Policy

Media and Politics and Canada

  Advance AND Venn diagram example

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Parts of this document were adapted, with permission, from materials originally developed by St. Paul's School (Concord, NH) in conjunction with McFarlin Library (University of Oklahoma, Tulsa); and the University of Pittsburgh, Pennsylvania whose help and generosity is gratefully acknowledged.

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