A Large-Scale Study of the Evolution of Web Pages
Dennis Fetterly
Hewlett Packard Labs
1501 Page Mill Road
Palo Alto, CA 94304
dennis.fetterly@hp.com
Mark Manasse
Marc Najork
Microsoft Research
Microsoft Research
1065 La Avenida
1065 La Avenida
Mountain View, CA 94043 Mountain View, CA 94043
manasse@microsoft.com najork@microsoft.com
Janet Wiener
Hewlett Packard Labs
1501 Page Mill Road
Palo Alto, CA 94304
janet.wiener@hp.com
ABSTRACT
1. INTRODUCTION
How fast does the web change? Does most of the content remain unchanged once it has been authored, or are the documents continuously updated? Do pages change a little or a lot? Is the extent of change correlated to any other property of the page? All of these questions are of interest to those who mine the web, including all the popular search engines, but few studies have been performed to date to answer them.
One notable exception is a study by Cho and Garcia-Molina,
who crawled a set of 720,000 pages on a daily basis over four months, and counted pages as having changed if their MD5 checksum changed. They found that 40% of all web pages in their set changed within a week, and 23% of those pages that fell into the
.com domain changed daily.
This paper expands on Cho and Garcia-Molina s study, both in terms of coverage and in terms of sensitivity to change. We crawled a set of 150,836,209 HTML pages once every week, over a span of
11 weeks. For each page, we recorded a checksum of the page, and a feature vector of the words on the page, plus various other data such as the page length, the HTTP status code, etc. Moreover, we pseudo-randomly selected 0.1% of all of our URLs, and saved the full text of each download of the corresponding pages.
After completion of the crawl, we analyzed the degree of change of each page, and investigated which factors are correlated with
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