Open Archive Initiative – Protocol for metadata Harvesting (OAI-PMH)

Surinder Kumar

Technical Director

NIC, New Delhi

suri@nic.in, 011-24305503

OAI-PMH

The mission of the Open Archives Initiative (OAI) (www.openarchives.org)

is to develop and promote “interoperability standards that aim to facilitate efficient

dissemination of content.

OAI-PMH

The OAI-PMH is based on a simple and powerful model “whereby repositories

(data providers) make metadata . . . available via a well-defined protocol.

The exposure of the metadata allows other organizations (service providers) to

harvest it and then aggregate it, post-process it, and refine it with the goal of developing

services that add value.

Background

Has origins in ePrints (arXive, CogPrints), dating back to 1999

– actively seeking wider applicability– Nothing to do with OAIS

Aims to “facilitate the efficient dissemination of content”

– free access to the archives (at least: metadata)– consistent interfaces for archives and service provider– low barrier protocol / effortless implementation (e.g., because

based on HTTP, XML, DC) Now on version 2.0 (June 2002)

OAI-PMH: what’s it all about

Service providers harvest metadata from data providers.

Requests (HTTP)

Metadata (XML)

Data provider

Metadata(+ resources)

Harv

est

er

Service Provider

Metadata“service”

Adapted from http://www.oaforum.org/tutorial/english/page3.htm

OAI PMH

What can be requested (verb)

Description of the archive (Identify) A list of metadata formats supported by the data

provider (ListMetadataFormats) A list of sets provided (ListSets) A list of resource identifiers (ListIdentifiers) Many records (ListRecords) An individual record (GetRecord)

Example Requests

http://archive.example.org/oaipmh?verb=Identify

http:// archive.example.org/oaipmh?verb=ListRecords&metadataPrefix=oai_dc

Metadata Formats

Metadata may be returned in any XML format Dublin Core is mandatory

– OAI-PMH specifies the XML schema to use– No single DC element is mandatory

Other element sets / bindings are optional– Qualified DC (e.g. RDN, NSDL)– MODS (LoC)– LOM (RDN-LTSN)– ODRL (JORUM (I think))– ...

Sets

A grouping of items made to allow selective harvesting– E.g. all theses– E.g. the Engineering section– E.g. all resources from a given source

Optional

List Records

Harvester can ask for specific metadata format for– All available items – All items in a set– All records modified in given date range– (A single item — GetRecord)

Data provider can return– All relevant records– Some relevant records + resumption token– An error code (no such set / metadata format)

Static Repositories

Even lighter-weight specification for data providers with small and relatively static collections– E.g. the output from a conference

Essentially an XML file available at a URL Accessed through a “static repository

gateway” intermediary

Issues: complexity

Providing data is easy Harvesting data is easyHowever Doing so may lead to complex workflow / policy

issues– What do you do with the harvested metadata?– Do you modify the metadata you harvest?– If so, do you feed this back to the provider?– What if the provider changes a modified record?– Does a service provider disseminate via OAI?

Issues: uptake

Lots of implementers, who have produced lots of useful support

However Relatively little commercial uptake Relatively little support for harvesting rich

metadata Relatively little support/consensus on sets

Issues: Harvesting resource (e.g. Full text)

Nothing in OAI-PMH requires that full-text should be available for harvesting.

– Resource may be physical or accessed controlled

Nothing in OAI-PMH requires that information required for harvesting should be available.

However in many cases OAI-PMH will provide the information required to harvest the resource.

http://www.myoai.co

Service Provider

Arc: A Cross Archive Search Servicehttp://arc.cs.odu.edu/From October 2000Arc is an experimental research service that serves as

a platform for demonstrating the scalability of the OAI-PMH and as a vehicle for providing access to OAI-compliant repositories through a unified search interface. Arc is the oldest federated search service based on the OAI-PMH.

OAISTER

OAIster is a union catalog of digital resources. We provide access to these digital resources by "harvesting" their descriptive metadata (records) using OAI-PMH (the Open Archives Initiative Protocol for Metadata Harvesting).

Service Providers

Citebasehttp://citebase.eprints.org/ May 2001Citebase “allows researchers to search across

free, full-text research literature eprint archives, with results ranked according to many criteria (e.g., citation impact), and then to navigate that literature using citation links and analysis.”

Contd…

SAIL-eprints (Search, Alert, Impact and Link)http://eprints.bo.cnr.it/April 2003 SAIL-eprints (Search, Alert, Impact and Link)

is “an electronic open access service provider for finding scientific or technical documents, published or unpublished, in Chemistry, Physics, Engineering, Materials Sciences, Nanotechnologies, Microelectronics, Computer Sciences, Astronomy, Astrophysics, Earth Sciences, Meteorology, Oceanography, . . . [Agriculture], and related . . . [subjects].”

Resources

Open Archives Initiative– http://www.openarchives.org/– Spec, best practice guide and useful resources, mailing lists

OAI for beginners– http://www.oaforum.org/tutorial/– Online tutorial

OAI Repository Explorer– http://www.purl.org/NET/oai_explorer– Web interface for issuing OAI-PMH requests