There are different kinds of search engines available today based their algorithms and the way in which they search and list the results. A search engine can described as a result generator by searching all the available documents, images, content, files, etc on the internet and list them according to the priority based on prior written algorithms. Based on the set of rules and the way it presents its results, search engine can be classified as crawler-based search engines, human powered directories, hybrid search engines and Meta search engines.
Crawler based search engines
The best example for crawler-based search engines is Google. The crawler based search engines create their listings automatically by ‘crawl’ or ‘spider’ the web. People use keywords to find out what they want to. The crawler based search engines use the keywords to search the billions of web pages and list them based on the location, previous searches and cookies of the computer to list the results.
The crawl bases search engines can find the changes in the websites and files, and can affect how those pages are listed. It provides importance to the page titles, content of the site, headings, bold and other special characters while searching for particular keywords. When queries, search engines do not even have a second to finish its processes, yet they have to complete all their big process within a fraction of second.
In the process the web server sends query to the index servers. The content of the index server is similar to the index in the back of a book. It provides the information of which book contains relevant phrases to the keywords. Finally the query is sent to the doc server, which retrieves the stored documents.
Human powered directories
The best example for human powered directories is “dmoz” which depends on humans for its listings. In the earlier stage Yahoo! Used the very method to produce results, now uses the crawl-based search listing method. In this process a directory gets information form submissions from the webmasters or site owners. The submission will include a short description to the directory about the site. Therefore changing contents in the web pages never make any changes in the search engine results.
Once the descriptions submitted to the search engine it tends to search which is very limited to the search description. There is nothing work to do with search engine optimization. The only way to get good ranking is to have a website with good navigation, content and information, as this will be more likely to get reviewed for free than a poor site.
Hybrid search engines
Hybrid search engine is kind of search engine which presents result from human edited web directories along with results that are generated by using algorithms. Now days it is a common kind of crawler type where human powered results will be combined with algorithm based search results, which actually favors one type of listings over another. The best example for hybrid search engine is MSN search which more likely present human powered listings along with crawler based results for obscure searches.
