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Publicly available Web services-such as Google, InfoSeek, Northernlight and AltaVista-employ various techniques to speed up and refine their searches. The three most common methods are known as preprocessing the data, "smart" representation and prioritizing the results.
One way to save search time is to match the Web user's query against an index file of preprocessed data stored in one location, instead of sorting through millions of Web sites. To update the preprocessed data, software called a crawler is sent periodically by the database to collect Web pages. A different program parses the retrieved pages to extract search words. These words are stored, along with the links to the corresponding pages, in the index file. New user queries are then matched against this index file.