The purpose of a search engine is to extract requested information from the huge database of resources available on the internet. Search engines become an important day to day tool for finding the required information without knowing where exactly it is stored. Internet usage has been tremendously increased in recent days with the easy to use search engines like Google, Bing and Yahoo!
Different Types of Search Engines
Search engines are classified into the following three categories based on how it works.
- Crawler based search engines
- Human powered directories
- Hybrid search engines / Meta Search Engines
Crawler based search engines
All crawler based search engines use a crawler or bot or spider for crawling and indexing the new content to the search database. There are four basic steps which every crawler based search engines follow before displaying any sites in the search results.
- Crawling
- Indexing
- Calculating Relevancy
- Retrieving the Result
Most of the popular search engines are crawler based search engines and use the above technology to display search results. Example of crawler based search engines:
- Google
- Bing
- Yahoo!
- Baidu
- Yandex
Human powered directories
A web directory or web guide is a hierarchical representation of hyper links. The top level of the directory typically provide a wide range of very general topics, such as arts, automobiles, education, entertainment, news, science, sports and so on. Each of these topics is a hyperlink that leads to more specialized sub-topics.
Directories are easy to use. Click or select the category for the topic in which you are interested, can continue to move down throw the hierarchy, selecting sub categories and narrowing the search at each level, until your are presented with a list of hyper links that pertain to your topic.
Examples: Yahoo, search.com, AOL
Meta Search Engines:
A meta search engine or all-in-one search engine performs a search by calling on more than one other search engine to do the actual work. The results are collected, duplicate retrievals are eliminated and the results are ranked according to how well they match user query.
The advantage of metal search engine is that you can access a number of different search engines with a single query.
The disadvantage is that you will often have high noise to signal ration; that is, a lot of the matches will not be of interest to you.
Dogpile is a search engine that fetches results from Google, Yahoo! and includes results from several other popular search engines.
Examples: metasearch.com, metacraeler.com
Sources / Further Reading
- https://www.webnots.com/what-are-different-types-of-search-engines/
- In-line / On-line Fundamentals of web tools and world wide web
