How Search Engines Work
The term "search engine" is often used generically to
describe both true search engines and directories. They are not the
same. The difference is how listings are compiled.
Search Engines Vs. Directories
Search Engines: Search engines, such as HotBot,
create their listings automatically. Search engines crawl the web, then
people search through what they have found.
If you change your web pages, search engines eventually find these
changes, and that can affect how you are listed. Page titles, body copy
and other elements all play a role.
Directories: A directory such as Yahoo depends on
humans for its listings. You submit a short description to the directory
for your entire site, or editors write one for sites they review. A
search looks for matches only in the descriptions submitted.
Changing your web pages has no effect on your listing. Things that
are useful for improving a listing with a search engine have nothing to
do with improving a listing in a directory. The only exception is that a
good site, with good content, might be more likely to get reviewed than
a poor site.
Hybrid Search Engines: Some search engines maintain
an associated directory. Being included in a search engine's directory
is usually a combination of luck and quality. Sometimes you can
"submit" your site for review, but there is no guarantee that
it will be included. Reviewers often keep an eye on sites submitted to
announcement places, then choose to add those that look appealing.
The Parts Of A Search Engine
Search engines have three major elements. First is the spider, also
called the crawler. The spider visits a web page, reads it, and then
follows links to other pages within the site. This is what it means when
someone refers to a site being "spidered" or
"crawled." The spider returns to the site on a regular basis,
such as every month or two, to look for changes.
Everything the spider finds goes into the second part of a search
engine, the index. The index, sometimes called the catalog, is like a
giant book containing a copy of every web page that the spider finds. If
a web page changes, then this book is updated new information.
Sometimes it can take a while for new pages or changes that the
spider finds to be added to the index. Thus, a web page may have been
"spidered" but not yet "indexed." Until it is
indexed -- added to the index -- it is not available to those searching
with the search engine.
Search engine software is the third part of a search engine. This is
the program that sifts through the millions of pages recorded in the
index to find matches to a search and rank them in order of what it
believes is most relevant.
Major Search Engines: The Same,
But Different
All search engines have the basic parts described above, but there
are differences in how these parts are tuned. That is why the same
search on different search engines often produces different results.
Information on
this page has been drawn from the help pages of each search engine,
along with knowledge gained from articles, reviews, books, independent
research, tips from others and additional information received directly
from the various search engines.
See also Meta Tags
See also Search Engine list
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