| Every day we use Internet services and search engines in particular when searching for information. The search results are usually called hits and are provided in the form of a list. The data may consist of web pages, images, data and other types of files. Some search tools also gather data available in databanks or open directories. If compared to Web directories which are maintained by human editors, search tools operate automatically or are a mixture of algorithmic and human input.
Web search tools function by storing information about numerous web pages which they retrieve from the INTERNET. These pages are retrieved by a web crawler, also known as a spider. It is an automatically-controlled Web browser that follows every link it finds. After that the content of each page is analyzed to determine how it should be indexed. Words, for instance, are extracted from titles, headings 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, store the whole or part of the source page (also called a cache) as well as data about web pages, while others, such as AltaVista, save and store every word of every page they have found. The cached page always contains the actual search text, because it is the one that was actually indexed. So, it can be very helpful because it comprises data that may no longer be available elsewhere.
When an Internet user types key words in the search field, the tool browse through its index and displays a list of the most suitable web pages in accordance with its criteria, commonly with a brief summary combined with the document's title and sometimes excerpts from the text. Some search engines have introduced an advanced tool called proximity search that allows users to define the length between search terms.
The usefulness of a search engine depends on the relevancy of the results it gives back. Since there can be millions of web pages containing a certain word or phrase, some pages may appear to be more relevant and popular than others. The results can be ranked to show the "best" ones first.
The way a search software program ranks web pages varies from one engine to another. The techniques also alter over time, because the use of Internet services undergoes alterations and advanced techniques are developed. |
