Transcript How much preservation do I get if I do absolutely nothing? Using the

How much preservation do I get
if I do absolutely nothing?
Using the Web Infrastructure for Digital Preservation
Michael L. Nelson, Frank McCown, Joan A. Smith, Martin Klein
Old Dominion University
Norfolk VA, USA
{mln,fmccown,jsmit,mklein}@cs.odu.edu
Media Production Berlin 2006
Berlin, Germany
December 8, 2006
Research supported in part by NSF, Library of Congress and Andrew Mellon Foundation
Preservation: Fortress Model
Five Easy Steps for Preservation:
1.
2.
3.
4.
5.
Get a lot of $
Buy a lot of disks, machines, tapes, etc.
Hire an army of staff
Load a small amount of data
“Look on my archive ye Mighty, and
despair!”
image from: http://www.itunisie.com/tourisme/excursion/tabarka/images/fort.jpg
Alternate 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
image from: http://www.proex.ufes.br/arsm/knots_interlaced.htm
Lazy Preservation
Research Questions
• How much digital preservation of websites is
afforded by lazy preservation?
– Can we reconstruct entire websites from the WI?
– What factors contribute to the success of website
reconstruction?
– Can we predict how much of a lost website can be
recovered?
– How can the WI be utilized to provide preservation of
server-side components?
Warrick: Crawling the Crawlers
• Is website reconstruction from WI feasible?
– Web repository: G,M,Y,IA
– Reconstructed 24 websites
• How long do search engines keep
cached content after it is removed?
SE Caching Experiment
•
•
•
•
Create html, pdf, and images
Place files on 4 web servers
Remove files on regular schedule
Examine web server logs to determine when
each page is crawled and by whom
• Query each search engine daily using
unique identifier to see if they have cached
the page or image
Joan A. Smith, Frank McCown, and Michael L. Nelson. Observed Web Robot Behavior on Decaying
Web Subsites. D-Lib Magazine, February 2006, 12(2)
Caching of HTML Resources mln
Reconstructing a Website
Original URL
Starting URL
Results page
Warrick
File
system
Retrieved
resource
Web Repo
Cached URL
Cached resource
1. Pull resources from all web repositories
2. Strip off extra header and footer html
3. Store most recently cached version or canonical version
4. Parse html for links to other resources
How Much Did We Reconstruct?
“Lost” web site
Reconstructed web site
A
A
B
D
B’
C
E
F
G
C’
F
E
Missing link to D;
points to old
resource G
F can’t
be found
Reconstruction Diagram
added
20%
identical
50%
changed
33%
missing
17%
Websites to Reconstruct
• Reconstruct 24 sites in 3 categories:
1. small (1-150 resources)
2. medium (150-499 resources)
3. large (500+ resources)
• Use Wget to download current website
• Use Warrick to reconstruct
• Calculate reconstruction vector
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.
Web Repository Contributions
100%
90%
80%
Contribution
70%
Yahoo
60%
IA
50%
MSN
40%
Google
30%
20%
10%
0%
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Reconstructed websites
Warrick Milestones
• www2006.org – first lost website reconstructed
(Nov 2005)
• DCkickball.org – first website someone else
reconstructed without our help (late Jan 2006)
• www.iclnet.org – first website we reconstructed
for someone else (mid Mar 2006)
• Internet Archive officially “blesses” Warrick (mid
Mar 2006)1
1http://frankmccown.blogspot.com/2006/03/warrick-is-gaining-traction.html
Shared Infrastructure
Preservation
(slightly less lazy)
Shared, Existing Infrastructure
• Can we (re)use existing installed network
infrastructure for preservation purposes?
Who has the Bigger Fortress?
Research Objective
• Premise: use common Internet Protocol implementations to
replicate repository contents
• Inject the contents of an OAI-PMH repository directly
into:
– Email (SMTP)
– Usenet News (NNTP)
• Instrument existing email, news servers
• Use mod_oai (www.modoai.org) to do resource harvesting
– complex object formats (e.g. MPEG-21 DIDL) used to encode the
resources as “lumps of XML”
– results are generalizable to any repository system
• Analyze testbed, simulate very large collections
Prototype Architecture
complex objects
Test Repository
• Website with 72 files
– HTML, PDF, PNG, JPEG, GIF
– 1KB - 1.5 MB
• Used a script to harvest the MPEG-21
DIDLs, and then:
– attach to outbound email mesgs
– post to a moderated newsgroup
(repository.odu.test1)
Email
Headers
OAI-PMH & HTTP
headers
original email mesg
base64 encoded DIDL
News
Posting
OAI-PMH & HTTP
headers
base64 encoded DIDL
Simulation Parameters
• Repository
–
–
–
–
100,000 items
1MB/item
100 daily additions
400 daily updates
• Time
– 2000 days (5.5 years)
• Email
– granularity=1
– follows ODU power
law example
• News
– servers hold contents
for 30 days
News Policies
NNTP Results
SMTP Policies
• passive, “piggybacking”
• History list of receiver domains
– not maintained; history pointer off
» duplicates
– maintained; history pointer on
» no duplicates
• Granularity Filter for emails
– every Gth email will be processed
SMTP Results
no history pointer
with history pointer
G=1
Summary
• Shared Infrastructure Preservation provides a
communications channel with unknown, future trading
partners
– SMTP approach is only feasible for “advertising” the existence of
the repository
– NNTP approach is promising for holding content
• Lazy Preservation has been used to restore several dozen
websites
– but is it an archival strategy? depends on your tolerance for risk
– prediction: search engines will see preservation as a business
opportunity