| Daily we use the Internet and search tools in particular when seeking data. The search results are commonly called hits and are provided in the form of a list. The data may contain web pages, images, data and other types of files. Some search engines also collect data available in databanks or open directories. Unlike Internet directories which are maintained by human editors, search tools work automatically or are a mixture of algorithmic and human input.
Web search tools function by storing data about countless web pages which they retrieve from the WWW. These pages are retrieved by An Internet crawler, also known as a spider. It is an automatically-controlled Web browser which follows every link it discovers. The content of each page is then analyzed to decide how it should be indexed. Words, for example, are removed from titles, headings and subheadings or special fields called meta tags. Data about web pages are saved and stored in an index databank for further use in queries. Some search engines, such as Google, store the whole or part of the source page (referred to as a cache) and information about web pages, whereas others, such as AltaVista, save and store every word of every page they have found. The cached page always contains the initial search text, since it is the one that was actually indexed. Therefore, it can be very useful when the content of the current page has been changed and the search terms are no longer in it.
Once a user has typed key words in the search field, the engine looks through its index and displays a listing of the most suitable web pages according to its parameters, normally with a short summary coupled with the title of the document and at times parts of the text. Some search tools provide an advanced feature called proximity search which allows users to define the distance between search terms.
The usefulness of a search engine rests on the relevance of the result set it provides. Since there can be millions of web pages containing a certain word or phrase, some pages may be more relevant and popular than others. The majority of search tools apply techniques to rank the results to feature the "best" results first.
How a search engine determines which pages are the best matches, and in what arrangement the results should be shown, varies from one engine to another. The methods also alter with time, as the use of the Internet undergoes alterations and advanced techniques appear. |
