1. Definitions and general data

1.1 Definitions

A search engine is a set of software programs designed to create a gigantic database of pages and documents, which are then made available to Internet users. These programs crawl the Web, automatically indexing the pages they visit, then analyzing them and returning the results they consider most relevant to the user's request.

Four steps are essential for a search engine to function properly:

• information gathering (or crawling) by robots (also known as spiders, crawlers or agents);

• indexing of collected data and creation of a document database known as an "index";

• query processing, with in particular a system for querying the...