Factors Affecting Website Reconstruction from the Web Infrastructure Frank McCown, Norou Diawara, and Michael L. Nelson Old Dominion University Computer.

Factors Affecting Website Reconstruction from the Web Infrastructure

Frank McCown, Norou Diawara, and Michael L. Nelson

Old Dominion UniversityComputer Science Department

Norfolk, Virginia, USA

JCDL 2007Vancouver, BCJune 20, 2007

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Outline

• Web-repository crawling with Warrick• How successful is a reconstruction?• Reconstruction experiment • Significant findings

3Black hat: http://img.webpronews.com/securitypronews/110705blackhat.jpgVirus image: http://polarboing.com/images/topics/misc/story.computer.virus_1137794805.jpg Hard drive: http://www.datarecoveryspecialist.com/images/head-crash-2.jpg

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Crawling the Crawlers

World Wide Web

Repo1

Repo2

Repon

...

Web crawling

Repo

Web-repository crawling

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Cached Image

Cached PDF

http://www.fda.gov/cder/about/whatwedo/testtube.pdf

MSN version Yahoo version Google version

canonical

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• McCown, et al., Brass: A Queueing Manager for Warrick, IWAW 2007.

• McCown, et al., Factors Affecting Website Reconstruction from the Web Infrastructure, ACM IEEE JCDL 2007.

• McCown and Nelson, Evaluation of Crawling Policies for a Web-Repository Crawler, HYPERTEXT 2006.

• McCown, et al., Lazy Preservation: Reconstructing Websites by Crawling the Crawlers, ACM WIDM 2006.

Available at http://warrick.cs.odu.edu/

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Measuring the Difference

(rc, rm, ra)

changed missing added

Apply Recovery Vector for each resource

Compute Difference Vector for website

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Some Difference Vectors

D = (changed, missing, added)

(0,0,0) – Perfect recovery

(1,0,0) – All resources are recovered but changed

(0,1,0) – All resources are lost

(0,0,1) – All recovered resources are at new URIs

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How Much Change is a Bad Thing?

Lost Recovered

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How Much Change is a Bad Thing?

Lost Recovered

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Assigning Penalties

Apply to each resource

(Pc, Pm, Pa)Penalty Adjustment

Or Difference vector

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Defining Success

success = 1 – dm

Equivalent to percent of recovered resources

0 1

Less successful

More successful

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Reconstruction Experiment

• 300 websites chosen randomly from Open Directory Project (dmoz.org)

• Crawled and reconstructed each website every week for 14 weeks

• Examined change rates, age, decay, growth, recoverability

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Success of website recovery each week

*On average, we recovered 61% of a website on any given week.

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Recovery of Textual Resources

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Recovery by TLD

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Birth and Decay

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Recovery of HTML Resources

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Recovery by Age

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Statistics for Repositories

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Which Factors Are Significant?

• External backlinks• Internal backlinks• Google’s PageRank• Hops from root page• Path depth• MIME type

• Query string params• Age• Resource birth rate• TLD• Website size• Size of resources

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Mild Correlations

• Hops and – website size (0.428)– path depth (0.388)

• Age and # of query params (-0.318)

• External links and – PageRank (0.339)– Website size (0.301)– Hops (0.320)

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Regression Analysis

• No surprises: all variables are significant, but overall model only explains about half of the observations

• Three most significant variables: PageRank, hops and age (R-squared = 0.1496)

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Conclusions

• Most of the sampled websites were relatively stable– One third of the websites never lost a single resource– Half of the websites never added any new resources

• The typical website can expect to get back 61% of its resources if it were lost today (77% textual, 42% images and 32% other)

• How to improve recovery from WI? Improve PageRank, decrease number of hops to resources, create stable URLs

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Thank You

Frank McCown

[email protected]://www.cs.odu.edu/~fmccown/

Sorry, Dad… You lost me in the first

two minutes.

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Injecting Server Components into Crawlable Pages

Erasure codesHTML pages Recover at least

m blocks

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Database

Perlscript

config

Static files (html files, PDFs,

images, style sheets, Javascript, etc.)

Web Infrastructure

Web Infrastructure

Web Server

Dynamicpage

Recoverable

Not Recoverable