There are various types of search on line and before we along this text you have to realize these differences. Four ideas you have to know:
- Search indexes or search engines: These are the principal type of
search tools you’ll run across. Originally, the expression search engine referred
to some type of search index, a huge database containing information
from individual Web sites. Google’s vast index (www.google.com) contains
over 3 billion pages, for example. Huge search-index companies
own thousands of computers that manage software known as spiders or robots
(or just plain bots - Google’s software is known as Googlebot) to capture
Web pages and read the information stored in them. These systems don’t
always snatch all the information on each page or all the pages in a Web
site, but they take a significant sum of information and use complex algorithms to index that information. Google is the world’s most popular search engine.
- Search directories: A directory is a categorized collection of information about Web sites. Rather than containing information from Web pages, it contains information about Web sites. The most considerable search directories
are owned by Yahoo! (dir.yahoo.com) and the Open Directory Project (www.dmoz.org). Directory companies don’t manage spiders or bots to download and index pages on the Web sites in the directory; rather, for each Web site, the directory contains information such as a title and description. The two most important directories, Yahoo! and Open Directory, have staff members who look at all the sites in the directory to make sure they are placed into the exact categories and meet guaranteed quality criteria. Less important directories often allow people submitting sites to detail which category must be used.
- Non-spidered indexes: I wasn’t clear in your mind what to call these things, so I made up a name: non-spidered indexes. A number of small indexes, less crucial than the major indexes such as Google, don’t manage spiders to examine the full contents of every page in the index. Rather, the index contains background information about every page, such as titles, descriptions,
and keywords. In various cases, this information comes from the meta tags pulled off the pages in the index. In other cases, the person who enters the site into the index provides this information.
- Pay-per-click systems: Certain systems provide pay-per-click listings. Advertisers place little ads into the systems, and when users execute their searches, the results contain some of these sponsored listings, typically above and to the right of the free listings.
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