The Open Archives Initiative
Michael L. Nelson
Computer Science, Old Dominion University
www.cs.odu.edu/~mln/
www.openarchives.org
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Open Archives Initiative
Protocol for Metadata Harvesting
• data providers / repositories:
o “A repository is a network accessible server that can
process the 6 OAI-PMH requests in the manner
described in [the OAI-PMH document]. A repository is
managed by a data provider to expose metadata to
harvesters.”
• service providers / harvesters:
o “A harvester is a client application that issues OAI-PMH
requests. A harvester is operated by a service provider
as a means of collecting metadata from repositories.”
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Data Providers / Service Providers
data providers service providers
(repositories) (harvesters)
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Overview of OAI-PMH Verbs
Verb Function
Identify description of repository
repository
metadata ListMetadataFormats metadata formats supported by repo
ListSets sets defined by repository
ListIdentifiers OAI unique ids contained in repo
harvesting
verbs ListRecords listing of N records
GetRecord listing of a single record
most verbs take arguments: dates, sets, ids, metadata formats
and resumption token (for flow control)
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

OAI-PMH data model
resource
OAI-PMH sets
OAI-PMH identifier entry point to all records pertaining to the resource item
OAI-PMH identifier Dublin Core MARCXML
metadataPrefix metadata records
metadata
datestamp
metadata pertaining
to the resource
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Complexity Comes to OAI-PMH…
• First noticed in how people would populate their Dublin Core records
o people need the HTML splash page
o crawlers need the PDF file
• Ad-hoc conventions and methods used to expose the repository’s
knowledge about the structure of the object
• Next three slides taken from “Resource Harvesting Within the
OAI-PMH Framework”
o http://www.dlib.org/dlib/december04/vandesompel/12vandesompel.html
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Dublin Core Encoding Type 1
<oai_dc:dc>
<dc:title>A Simple Parallel-Plate Resonator Technique for Microwave.
Characterization of Thin Resistive Films</dc:title>
<dc:creator>Vorobiev, A.</dc:creator>
<dc:subject>ING-INF/01 Elettronica</dc:subject>
<dc:description>A parallel-plate resonator method is proposed for
non-destructive characterisation of resistive films used in
microwave integrated circuits. A slot made in one ... </dc:description>
<dc:publisher>Microwave engineering Europe</dc:publisher>
<dc:date>2002</dc:date>
<dc:type>Documento relativo ad una Conferenza o altro Evento</dc:type>
<dc:type>PeerReviewed</dc:type>
<dc:identifier>http://amsacta.cib.unibo.it/archive/00000014/</dc:identifier>
<dc:format>pdf
http://amsacta.cib.unibo.it/archive/00000014/01/GaAs_1_Vorobiev.pdf
</dc:format>
</oai_dc:dc>
splash page locator of resource
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Dublin Core Encoding Type 2
…
<dc:identifier>http://amsacta.cib.unibo.it/archive/00000014/</dc:identifier>
<dc:relation>
http://amsacta.cib.unibo.it/archive/00000014/01/GaAs_1_Vorobiev.pdf
</dc:relation>
…
splash page locator of resource
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Dublin Core Encoding Type 3
…
<dc:identifier> http://amsacta.cib.unibo.it/archive/00000014/</dc:identifier>
<dc:relation>
http://resolver.unibo.it/00000014/
</dc:relation>
<dc:relation>
http://amsacta.cib.unibo.it/archive/00000014/01/GaAs_1_Vorobiev.pdf
</dc:relation>
…
splash page
locator of resource
splash page
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

OAI Object Re-Use and Exchange
• Develop, identify, and profile extensible standards and protocols to
allow repositories, agents, and services to interoperate in the
context of use and reuse of compound digital objects beyond the
boundaries of the holding repositories.
• Aim for more effective and consistent ways:
o to facilitate discovery of these objects,
o to reference (link to) these objects (and parts thereof),
o to obtain a variety of disseminations of these objects,
o to aggregate and disaggregate these objects,
o Enable processing by automated agents
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

The Structure of Compound Objects is Obfuscated
When Mapped to the Web
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Useful for humans and useful for applications is often different
HTTP LINK HEADER
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Through the Resource Map, the Web application sees the compound object
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

This approach reveals compound objects in the Web graph
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

OAI: Its Not Just for
Metadata Harvesting Anymore…
OAI-PMH OAI-ORE
Repository structure Object structure
Metadata centric Resource centric
Metadata harvesting Object re-use (obtain,
harvest, register)
OAI-PMH and OAI-ORE are complimentary;
o you can do one without the other
o you can do them together
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

OAI-ORE : Current Status
• Ongoing definition of the ORE framework
o Reach joint problem statement
o Issues regarding identification
o Model for ORE resource
o Publishing ORE resources to the Web
o Discovering ORE resources
• Review of appropriate technologies for ORE Model and Resource
Map
o ATOM
o DID/DIDL, IMS/CP, METS, Ramlet
o RDF, RDF/XML
o Dublin Core Abstract Model
o …
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

OAI-ORE : Current Status
• Explore demonstrators using these concepts in preparation of May
2007 ORE Technical Committee meeting
• Post May 2007 meeting:
o Hopefully work towards alpha specs for ORE resource, Resource Map,
discovery of ORE resource
o Experimentation with alpha specs
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

My research group’s approach to
OAI/Preservation integration…
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Preservation: Fortress Model
Five Easy Steps for Preservation:
1. Get a lot of $
2. Buy a lot of disks, machines, tapes,
etc.
3. Hire an army of staff
4. Load a small amount of data
5. “Look upon my archive ye Mighty, and
despair!”
image from: http://www.itunisie.com/tourisme/excursion/tabarka/images/fort.jpg
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Alternate Models
of Preservation
• Lazy Preservation
o Let Google, IA et al. preserve your website
• Just-In-Time Preservation
o Wait for it to disappear first, then a “good enough”
version
• Shared Infrastructure Preservation
o Push your content to sites that might preserve it
• Web Server Enhanced Preservation
o Use Apache modules to create archival-ready resources
image from: http://www.proex.ufes.br/arsm/knots_interlaced.htm
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Web Site Preservation: 2 Problems
Guess the bean count,
win the jar
The counting problem The representation problem
How many pages are on that site? What’s that page all about?
To save it you have to find it Future use requires understanding
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

OAI-PMH Data Model
resource
OAI-PMH identifier item
= entry point to all records pertaining to the resource
metadata pertaining Dublin Core MPEG-21 MARCXML records
to the resource metadata METS
DIDL metadata
modeled representation simple complex complex more expressive
of the resource model model model model
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

mod_oai implementation
Integrate OAI-PMH functionality into the web server itself…
1. Use mod_oai
- an Apache 2.0 module
- automatically answers OAI-PMH requests for an http server
- written in C
- respects values in .htaccess, httpd.conf
2. Install mod_oai on http://www.foo.edu/
Define baseURL: http://www.foo.edu/modoai
3.
Result: web harvesting with OAI-PMH semantics (e.g., from, until, sets)
http://www.foo.edu/modoai?verb=ListRecords&metdataPrefix=oai_didl&from=2004-09-15&set=mime:video:mpeg
From site foo, dating from 9/15/2004 through today
Give me all resources
Using OAI-PMH
And their preservation metadata that are MIME type video-MPEG
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Addressing the Counting Problem: ListIdentifiers
CRAWLER:
• issues a ListIdentifiers,
• finds URLs of updated
resources
• does HTTP GET updates
only
• can get URLs of resources
with specified MIME
types
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Addressing the Representation Problem: ListRecords in DIDL Format
CRAWLER:
• Makes a ListRecords
query,
• Gets updates as MPEG-21
DIDL records (HTTP
headers, resource By
Value or By Reference)
• can get resources with
specified MIME types
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

CRATE: Preservation Metadata at Dissemination Time
• Harnesses web
server to support
preservation
• Moves preservation
metadata from
“strict validation at
ingest”
to “best-effort Plug-in Name Executable path
description at
dissemination”
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson

Validation is Subjective
Preservation metadata is like a David Hockney photo collage:
each image is both true and incomplete,
and while the result is not faithful, it does capture the “essence”
images from: http://facweb.cs.depaul.edu/sgrais/collage.htm
The Open Archives Initiative
DRIADE Workshop, Durham NC, May 16-17, 2007
Michael L. Nelson