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A Web Search Engine: General Information |
| Date Added: October 17, 2009 07:35:23 PM |
| Author: Martin |
| Category: Computers & Internet: Search Engine Optimization |
| A web search engine is a software program specially-designed to search for data on the Web. The search results are commonly provided in the form of a list and are commonly called hits. The data may consist of web pages, images, information and other types of files. Some search tools also accumulate data available in databanks or open directories. In comparison with Web directories which are maintained by human editors, search tools function automatically or are a mixture of algorithmic and human input. Internet search tools function by storing data about numerous web pages which they retrieve from the WWW. These pages are retrieved by a web crawler, also known as a spider. It is an automated Web browser which follows every link it discovers. The content of each page is then analyzed to decide how to index it. Words, for instance, are extracted from titles, headings and subheadings or special fields called meta tags. Data about web pages are saved and stored in an index database for further use in queries. Some search engines, such as Google, save and store the entire or part of the source page (known as a cache) as well as information about web pages, whereas others, such as AltaVista, store every word of every page they discover. The cached page always comprises the actual search text, because it is the one that was actually indexed. Thus, it can be very helpful when the content of the current page has been changed and the search terms are no longer in it. When an Internet user types search terms in the search field, the engine looks through its database and displays a list of best-matching web pages in accordance with its parameters, commonly with a brief summary containing the title of the document and sometimes parts of the text. Some search engines have installed an advanced option called proximity search which allows users to define the length between search words. The usefulness of a search engine hinges on the relevance of the results it provides. Since there can be millions of web pages that contain a certain word or word combination, web pages can be divided into relevant and irrelevant ones. The vast majority of search tools use methods to rank the results to display the "best" results first. How a search engine determines which pages are the best matches, and in what arrangement the results should be displayed, differs from one engine to another. The techniques also change with time, because the use of Internet services alters and advanced techniques are invented. |
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