Search Engines are programs which search the web. Web is a big graph along with the pages being the nodes & hyperlinks being the arcs. Search engines gather all the hyperlinks on each of the page they read, eliminate all the ones which have already been processed & save the rest. Then the Web is searched breadth-first that means each of the links on page is followed and all of the hyperlinks on all the pages pointed to are gathered but they are not traced in the order obtained. Automated search is the service which is provided through Search engines. An automated search service lets an individual to determine information which resides on remote computers. Automated search systems employ computer programs to determine web pages which contain information related to a given topic. It let to locate:
- Web pages linked with a particular company or individual
- Web pages which contain information about a particular product.
- Web pages which contain information regarding a particular topic.
The results of an automated search can be immediately used or stored into a file on disk to employ it later. The results of a search are returned in form of a web page which has a link to each of the items that was found. Automated search is helpful while a user wished to explore a new topic. The automated search generates a list of candidate pages which may contain information. The user reviews each of the pages in the list to see whether the contents are associated to topic or not. If so, the user records the location or if not user moves on to the page in the list. Search mechanisms employ a similar method of search as in the telephone book that means before any user invoke the search mechanism a computer program contacts computers on the Internet, collect a list of obtainable information, sorts the list and then stores the result on a local disk on the computer which runs a search server. While a user invokes a search, the user client program which contacts the server. The client sends request which contains the name the user entered. While the request arrives at the server, it consults the list of file names on its local disk & provides the result.