Search engine in the operating sequence is as follows:
1) Crawling,
2) Deep Crawling Depth-first search (DFS),
3) Crawling Fresh Breadth-first (BFS);
4) Indexing,
5) search.
Search engines work by storing information about many web pages, they took from the WWW itself. These pages are retrieved by a web crawler (also known as a spider) - an automated web browser which follows every link it sees, an exception can be made using robots.txt. The contents of each page and then analyzed to determine how it should be indexed. Data about web pages are stored in an index database for use in later queries. Some search engines such as Google, store all or part of the page source (called a cache) as well as information on the web page, whereas some store every word of every page it finds, such as AltaVista.
