Search Engines

What is a search engine?

A search engine is an information retrieval system designed to help find information stored on a computer system.

What is a Web search engine?

A Web search engine is specific to the World Wide Web. Information may consist of web pages, images, or other types of files. Some search engines also mine data from newsbooks, databases, or open directories. Unlike Web directories, which are managed by human editors, search engines do not need human intervention. Humans program algorithms that retrieve results. Sometimes, search engines are a mix of direct human intervention and algorithms.

Examples of Search Engines

Yahoo! Search:

What do they have in common?
  • The default Boolean operator AND - if you type in two or more words, you don't need to use AND as a Boolean operator in any of these search engines.
    • example: acid rain is treated as acid AND rain without the Boolean operator
  • The Boolean operator OR, if you enter it in capital letters so the system doesn't think this is just a word.
    • example: acid OR rain
NOTE: If you use a Boolean operator in any of these search engines, BE SURE TO USE ALL CAPITAL LETTERS.
  • The capability of excluding words, but you can't always just use NOT.
    • In Google, Yahoo, and, you must use a hyphen and there must be no space betwen the hyphen and the word you wish to exclude;
      • example for Google, Yahoo, and acid -rain
    • in Exalead and Gigablast you can use NOT, AND NOT, or a hyphen. This is useful if you are looking for information about acid from a chemistry perspective, for example, and don't want acid rain for this particular search
      • examples for Exalead and Gigablast:
        • acid NOT rain
        • acid AND NOT rain
        • acid -rain
  • Adjacency: if you enter a phrase in quotation marks, e.g. "acid rain," you will retrieve only those results where acid and rain are next to each other. The system searches for the following string of characters: a c i d blank r a i n
    • Example: "acid rain"
  • Nesting: to tell the system in what order to execute your search string. There are several ways to do that.
    • One is to use quotation marks around the parts you want to appear together and enter them with another term you want
      • Example: "acid rain" chemistry
    • Another is to use parentheses around the part you want searched first
      • Example: (acid rain) chemistry (NOTE: in this case, the system is searching acid AND rain first and then combining the results with a search for chemistry, so you will get more results than in the previous example
  • Stop words: these ignore common words, such as the, a, etc.
    • Example: Jump the shark will search jump shark
  • Include common words: you can use quotations for this or put plus signs between the words (no spaces)
    • Example: jump+the+shark; "jump the shark"
What about differences?
  • Size: the number of web sites that are searched
    • Google: probably the largest, although in 2007, Yahoo! Search did an upgrade and claimed to be the largest. In our assignment posted January 7, one of our students found that out, as I saw on the student's blog.
    • Yahoo! Search: approx. 22 billion
    • over 2 billion
    • Exalead: over 8 billion
    • Gigablast: over 12 billion
  • Default rankings: how the web sites are ordered when they show up on your screen
    • Google: by popularity
    • Yahoo! Search, Exalead, Gigablast: by relevancy
    • by same-subject popularity
  • Modifying default rankings: there are ways to change how the search engine lists the results
    • Google: view:timeline; view:info, view:map
    • Exalead: click "only recent results" at top of search results; date sorts in "Advanced Search" by oldest or newest, or you can use sort:old or sort:new
    • Gigablast: Pipe between terms ranks by the term after the pipe, e.g. acid|rain will rank by the word rain
    • Yahoo! Search, no modification
  • Search suggestions: search engines will try to give you "hints" of various kinds
    • Google: sometimes gives search suggestions in results, e.g., for mis-spellings
    • Yahoo! Search: suggests related searches if other Yahoo searchers have searched the same topic
    • suggests narrower or broader search terms
    • Exalead: offers Narrow your search to focus the search in many ways
    • Gigablast: provides Giga Bits at the tops of the results to reflect the main themes in the results
There are other tips and tricks you can apply to search engines, but you have to know which tip or trick applies to which search engine. The ones I've provided above are probably the most common ones you will need.