How Do Search Engines Work? Dr. Steve Broskoske Misericordia
University
Slide 3
Do search engines actually search the entire Web when you enter
search terms?
Slide 4
Yes and no. Yes, it does search the entire world. But not when
you hit the search button. The search was already done in
advance.
Slide 5
How do search engines actually work?
Slide 6
Without using a computer, how would you search out all of the
people named Smith in the Wyoming Valley area? Use the phone book!
Analogy
Slide 7
Search engines create an index, analogous to a phone book. When
you search, you actually search the index! Word No. of Times URL
technology 15 http://www.somewhere technology 12
http://www.somewhere terabyte 4 http://www.somewhere
Slide 8
Do search engines all produce the same quality of results?
Slide 9
No! The quality of results depends on the quality of the index.
Indexes are not all the same! Read part of Web page. Read more of
Web page. Read all of Web page. Also: Some indexes are arranged by
humans, and others by computer algorithm.
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How do Web pages make it into a search engine?
Slide 11
Web pages make it to a search engine through: 1.Web crawlers
Software that searches the Web and indexes Web pages. 2.Voluntary
submission.
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Why can I sometimes not find the words I searched for?
Slide 13
Why you cant find search terms on Web pages: Web page content:
Has been changed. Has been renamed or removed. Better search
engines cache a copy of the page when they index it. The search
terms were found on this page when this page was cached.
Slide 14
Does any information hide from search engines? There is much
information that cannot be indexed by Web crawlers. This is know as
the: Dynamically generated Web pages. Databases. (Contents of PDF,
PowerPoint, and Word documents used to be non-searchable.)
Invisible Web Some search engines are designed to locate
information on the invisible/deep Web.
Slide 15
Review Search engines read all of the Web pages in the world,
and index them. When you search, you are querying a search engines
index. Much of the Web is unsearchable (called the invisible Web).
Knowing how search engines work makes you a better searcher.
