Lazy Preservation, Warrick, and the Web Infrastructure Frank McCown Old Dominion University Computer Science Department Norfolk, Virginia, USA JCDL 2007.

Lazy Preservation, Warrick, and the Web Infrastructure

Frank McCown

Old Dominion UniversityComputer Science Department

Norfolk, Virginia, USA

JCDL 2007Vancouver, BCJune 19, 2007

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Outline

• What is the Web Infrastructure (WI)?• How can the WI be used for preservation?• Web-repository crawling with Warrick• Understanding the WI

– Caching experiment– Reconstruction experiments– Search engine sampling and IA overlap experiment

• Recovering web server components from the WI• Brass: Queueing manager for Warrick

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Web Infrastructure

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Alternative Models of Preservation

• Lazy Preservation– Let Google, IA et al. preserve your website

• Just-In-Time Preservation– Wait for it to disappear first, then a “good enough”

version

• Shared Infrastructure Preservation– Push your content to sites that might preserve it

• Web Server Enhanced Preservation– Use Apache modules to create archival-ready

resources

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7Black 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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Web-repository Crawler

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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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What Types of Websites Are Lost?

Marshall, McCown, and Nelson, Evaluating Personal Archiving Strategies for Internet-based Information, IS&T Archiving 2007.

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Outline

• What is the Web Infrastructure (WI)?• How can the WI be used for preservation?• Web-repository crawling with Warrick• Understanding the WI

– Caching experiment– Reconstruction experiments– Search engine sampling and IA overlap experiment

• Recovering web server components from the WI• Brass: Queueing manager for Warrick

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Understanding the WI

• How quickly do search engines acquire and purge their caches?

• Do search engines prefer caching one type of resource over another?

• How much overlap is there between the search engines caches and IA holdings?

• How successfully can we reconstruct a lost website?

• Are some resources more recoverable than others?

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Timeline of Web Resource

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Web Caching Experiment

• Create 4 websites composed of HTML, PDFs, and images– http://www.owenbrau.com/– http://www.cs.odu.edu/~fmccown/lazy/– http://www.cs.odu.edu/~jsmit/– http://www.cs.odu.edu/~mln/lazp/

• Remove pages each day

• Query GMY every day using identifiers

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

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Where is the Internet Archive?

• No crawls from Alexa, IA’s provider

• Even if they had crawled us, the content would not be accessible from IA for 6-12 months

• Short-lived web content is likely to be lost for good

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2005 Reconstruction Experiment

• Crawl and reconstruct 24 sites of various sizes:

1. small (1-150 resources) 2. medium (151-499 resources)3. large (500+ resources)

• Perform 5 reconstructions for each website– One using all four repositories together– Four using each repository separately

• Calculate reconstruction vector for each reconstruction (changed%, missing%, added%)

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How Much Did We Reconstruct?

A

“Lost” web site Reconstructed web site

B C

D E F

A

B’ C’

G E

F

Missing link to D; points to old resource G

F can’t be found

Four categories of recovered resources:

1) Identical: A, E2) Changed: B, C3) Missing: D, F4) Added: G

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Reconstruction Diagram

added 20%

identical 50%

changed 33%

missing 17%

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Recovery Success by MIME Type

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Repository Contributions

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2006 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

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

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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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Statistics for Repositories

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Experiment: Sample Search Engine Caches

• Feb 2006

• Submitted 5200 one-term queries to Ask, Google, MSN, and Yahoo

• Randomly selected 1 result from first 100

• Download resource and cached page

• Check for overlap with Internet Archive

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

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Distribution of Top Level Domains

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Cached Resource Size Distributions

976 KB 977 KB

1 MB 215 KB

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Cache Freshness

crawled and cached

changed on web server

crawled and cached

Stale

time

Fresh Fresh

Staleness = max(0, Last-modified http header – cached date)

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Cache Staleness

• 46% of resource had Last-Modified header

• 71% also had cached date

• 16% were at least 1 day stale

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Similarity vs. Staleness

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How much of the Web is indexed?

Estimates from “The Indexable Web is More than 11.5 billion pages” by Gulli and Signorini (WWW’05)

Google

Yahoo

MSNIndexable

Web

8 billion pages

6.6 billion pages

5 billion pages

11.5 billion pages

Internet Archive?

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Overlap with Internet Archive

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Overlap with Internet Archive

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Distribution of Sampled URLs

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Problem:

WI currently only stores the client-side representation of a website. Server components (scripts, databases, configuration files, etc.) are not

accessible from the WI

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Outline

• What is the Web Infrastructure (WI)?• How can the WI be used for preservation?• Web-repository crawling with Warrick• Understanding the WI

– Caching experiment– Reconstruction experiments– Search engine sampling and IA overlap experiment

• Recovering web server components from the WI• Brass: Queueing manager for Warrick

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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

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Injecting Server Components into Crawlable Pages

Erasure codesHTML pages Recover at least

m blocks

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Brass: A Queueing Manager for Warrick

• Warrick requires some technical expertise to download, install, and run

• Warrick uses search engine APIs which allow limited requests per IP address (or key)

• Google no longer provides new keys for accessing their API

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Thank You

Frank McCown

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

Can’t wait until I’m old enough to

recover a website!

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Cache Freshness

crawled and cached

changed on web server

crawled and cached

Stale

time

Fresh Fresh

Staleness = max(0, Last-modified http header – cached date)

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Cache Staleness

• 46% of resource had Last-Modified header

• 71% also had cached date

• 16% were at least 1 day stale

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Similarity vs. Staleness

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Web Repository CharacteristicsType MIME type File ext Google Yahoo Live IA

HTML text text/html html C C C C

Plain text text/plain txt, ans M M M C

Graphic Interchange Format image/gif gif M M M C

Joint Photographic Experts Group

image/jpegjpg

M M M C

Portable Network Graphic image/png png M M M C

Adobe Portable Document Format

application/pdfpdf

M M M C

JavaScript application/javascript js M M C

Microsoft Excel application/vnd.ms-excel xls M ~S M C

Microsoft PowerPoint application/vnd.ms-powerpoint

pptM M M C

Microsoft Word application/msword doc M M M C

PostScript application/postscript ps M ~S C

C Canonical version is storedM Modified version is stored (modified images are thumbnails, all others are html conversions)~S Indexed but not stored

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Results

Frank McCown, Joan A. Smith, Michael L. Nelson, and Johan Bollen. Reconstructing Websites for the Lazy Webmaster, Technical Report, arXiv cs.IR/0512069, 2005.