Q. Basic need of Search Engines?

Search Engines are programs which search the web. Web is a big graph with pages being the nodes and hyperlinks being the arcs. Search engines collect all hyperlinks on each page they read, remove all the ones which have already been processed and save the rest. Web is then searched breadth-first, i.e. every link on page is followed and all the hyperlinks on all the pages pointed to are collected however they aren't traced in the order obtained. Automated search is the service which is provided by Search engines. An automated search service enables an individual to find information that resides on remote computers. Automated search systems use computer programs to find web pages that comprise information related to a given topic. It allows to locate:

• Web pages which contain information about a particular product.
• Web pages associated with a particular company or individual
• Web pages which contain information about a particular topic.

Results of an automated search can be used immediately or stored in a file on disk to use it later. Results of a search are returned in the form of a web page that has a link to each of the items that was found. Automated search is helpful when a user wants to explore a new topic. Automated search produces a list of candidate pages which may contain information. The user reviews every page in the list to see whether contents are related to topic or not. If so, user records the location or if not user moves on to the page in the list. Search mechanisms uses a similar method of search as in telephone book i.e. before any user invoke search mechanism a computer program contacts computers on the Internet, gathers a list of available information, sorts the list and then stores result on a local disk on computer which runs a search server. When a user invokes a search, user client program which contacts the server. Client sends a request which contains the name the user entered. When request arrives at the server, it consults that list of file names on its local disk and provides the result.