The Boolean model is one of many information retrieval models.  It is identified in our text (Modern Information Retrieval) as one of the three classic unstructured text models.

It is a very simple model and easy to implement.  This model is based on whether an index term is present or not.  The simplicity of this model leads to several of its disadvantages.  It only retrieves exact matches and there is no ranking of documents.  Historically it is the most common model, used by library online public access catalogs (OPACs) and many web search engines.

Boolean search operators are “AND”, “OR”, and “NOT”.  The “AND” operator is used to narrow a search by combining teams.  Only documents containing both search terms a user specifies are returned.  The “OR” operator is used to broaden a search so that documents containing either of the terms a user provides are returned.  The “NOT” operator narrows a search by excluding certain search terms, by returning documents containing the term before the operator, but not the term after.  Other Boolean search symbols include quotation marks, which specify phrases between them are to be searched for exactly as they are written, and the “*” symbol, which is used for wildcard searching.

Many search engines now incorporate some type of page ranking mechanism.  For example, one algorithm used by Google is PageRank.  I located the following information about PageRank by using the term “pagerank” in the Yahoo search engine. The Wikipedia article on PageRank was the second on this list of items returned.   PageRank counts the number and quality of links to a web page to determine a rough estimate of that site’s importance using the assumption that more important web pages will receive more links from other web pages.

One example of a company that uses a traditional Boolean search model is Westlaw.  I located this YouTube video by using the search term “examples of Boolean information retrieval models” on Chrome using Yahoo as the search engine.  A link to the video was the 8th option returned.  Westlaw provides an online legal research service to more than half a million subscribers.  Many professional searchers prefer Boolean queries because it gives them more control over the results received.  However, most users find it awkward and difficult to use Boolean expressions.

Google Advanced Search offers an easy way to use Boolean operators.  Instructions on how to enter terms in the boxes are included on the right side of the screen.

Google advanced search 2

Yahoo also offers an advanced web search along these same lines.

I typically use Google as my search engine; however I do not use the Google Advance Search feature.  I usually type the search term I want to find information on into the search box such as I described above (although my browser currently defaults to the Yahoo search engine – must change that since I prefer Google!).  Now that I have learned more about Boolean operators, I definitely plan to use them more often when I search the internet!