INTERNET SEARCH ENGINES
Search engines use software called spiders to search for documents on the World Wide Web (WWW). Indexing software then extracts information from the document and stores it in a database. The type and depth of indexing depends upon the particular search engine, most include the document web address and keywords. When a user performs a search, the database is searched for matching documents. The results are presented according to the search engine's ranking criteria, which also varies among search engines.
DIFFERENCES AMONG SEARCH ENGINES
SIZE OF SEARCH ENGINES
Currently, no one search engine is capable of searching the entire WWW. Among the numerous search engines, there are significant differences in size of indices (e.g. the WWW content that has been indexed and added to their respective databases). Fast, currently leads as the largest database with over 500 million URLs indexed, followed by NorthernLight and AltaVista. Large search engine databases will give you access to the largest number of web-based documents.
SORTING OF SEARCH RESULTS
In addition to the size of a search engine's database, the method of ranking and presenting search results becomes important when faced with hundreds of hits of questionable value. Most search engines employ a relevancy ranking criteria; Google is unique in that it also factors in the document's popularity (how often it is linked to) as a measure of its usefulness.
SEARCH FEATURES OF SEARCH ENGINES
While many search engines have limited search features, some search engines allow for the use of Boolean operators and field restrictors to improve search precision.
Example: Search Engine Features Chart This page compares the search features of leading search engines.
However, syntax may vary among search engines. Additionally, some search engines are case sensitive; some search engines automatically account for plural forms of words; some use AND as a search default others use OR. Check each engine's help or search tips page to see what search features they support and the search syntax used.
Example: Dogpile Tips and Tricks
SPECIALIZED SEARCH ENGINES
Specialized search engines tailored towards specific subjects are becoming increasingly common. Examples for the topic of law:
Metasearch engines perform search queries simultaneously on multiple search engines. When using a metasearch engine, be sure to review the search syntax rules since you are effectively searching numerous search engines, each of which might have slightly different search syntax.
Web directories are selective collections of web resources arranged by subject. Typically, directory editors review web submissions, with selectivity and focus varying among the directories. Yahoo! has a well-known directory with an obvious commercial focus. However, there are numerous other specialized directories with an academic focus: A few examples are:
Portals serve as gateways or starting points to the WWW. They often include multiple features, such as web directories, search engine access, email service, news, etc. Examples of portal sites: Yahoo!, CNET.