Daily we use Internet services and search tools in particular when looking for information. The search results are usually provided in the form of a list and are commonly called hits. The information may comprise web pages, images, data and other types of files. Some search engines also gather data available in databanks or open directories. If compared with Web directories that are maintained by human editors, search tools work automatically or are a mix of algorithmic and human input. Web search tools work by storing data about countless web pages which they retrieve from the WWW. These pages are retrieved by a web crawler, or differently called 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 decide how to index it. Words, for example, are removed from titles, headings or special fields called meta tags. Data about web pages are stored in an index databank for further use in queries. Some search tools, such as Google, save and store the whole or part of the source page (differently called a cache) as well as data about web pages, while others, such as AltaVista, save and store every word of every page they discover. This cached page always comprises the actual search text, since it is the one that was actually indexed. Thus, it can be very useful because it includes data that may no longer be available elsewhere. Once an Internet user has typed key words in the search field, the engine checks its catalogue and shows a listing of the most suitable web pages in accordance with its criteria, commonly with a brief summary coupled with the title of the document and at times excerpts from the text. Some search tools provide an advanced feature called proximity search which allows users to define the distance between key words. The usefulness of a search engine hangs on the relevance of the result set it gives back. Since there may be millions of web pages containing a particular word or word combination, some pages may appear to be more relevant and popular than others. The majority of search engines employ techniques to rank the results to show the "best" results first. The way a search engine shows web pages is specific to a search engine. The techniques also change over time, since the use of Internet services undergoes alterations and advanced techniques are developed. |
