题目内容
URLs from the frontier need visiting only once.
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To prioritize its downloads means to determine the order according to their relative importance.
The heavy task of a Web crawler lies in the large volume of Web pages, their high rate of change and the difficulty to avoid retrieving duplicate content.
Endless combinations of HTTP GET (URL-based)parameters are useful for the crawler to get unique content.
Combinations of HTTP GET (URL-based)parameters can produce different URLS, all of which may be linked on the site.
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