| A web search engine is a software program designed to search for information on the Web. The search results are commonly called hits and are provided in the form of a list. The data may contain web pages, images, information and other types of files. Some search engines also collect data available in databases or open directories. Unlike Internet directories which are maintained by human editors, search tools work automatically or are a mix of human and algorithmic input.Web search engines function by storing data about a huge number of web pages which they retrieve from the INTERNET. These pages are retrieved by a web crawler, or differently called a spider. It is an automatically-controlled Web browser which follows every link it finds. The content of each page is then analyzed to decide how to index it. Words, for instance, are removed from titles, headings and subheadings or special fields called meta tags. Data about web pages are saved and stored in an index catalogue for further use in queries. Some search engines, such as Google, save and store the whole or part of the source page (known as a cache) and information about web pages, whereas others, such as AltaVista, store every word of every page they find. The cached page always comprises the initial search text, because it is the one that was actually indexed. So, it can be very helpful when the content of the current page has been altered and the search words are no longer in it.As soon as a user has typed key words in the search field, the engine checks its index and shows a list of the most suitable web pages in accordance with its parameters, commonly with a short summary containing the document's title and at times excerpts from the text. Some search tools have installed an advanced tool called proximity search which allows users to determine the length between search terms.The usefulness of a search engine hinges on the relevance of the results it provides. Since there may be millions of web pages containing a particular search term or phrase, some pages may appear to be more relevant and popular than others. The vast majority of search engines apply methods to rank the results to feature the "best" results first.The way a search software program displays web pages is search engine-specific. The techniques also alter in time, as the use of the Internet changes and new techniques are employed. |
