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A brief introduction to the OAI-PMH protocol with links to further information.

OAI-PMH

OAI-PMH is a protocol for exposing metadata so it can be harvested and used by search services.  The Open Archives Initiative (OAI) developed the protocol to provide an interoperability framework for e-print repositories, but it can be applied to a wide range of digital materials.

What it is

The Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) is a protocol for exposing metadata so it can be harvested and used by search services.  Basically the protocol specifies that Dublin Core metadata is transmitted in XML format via HTTP.

How it Works

A ‘data provider’ builds an OAI-compliant repository and uses the protocol to expose its metadata.  A ‘service provider’ then uses the same protocol to harvest the metadata.  Typically the service provider harvests metadata from several sources.  Once the metadata is aggregated, the service provider then uses it to provide services.  A search service based on the aggregated metadata effectively allows users to cross-search the separate sources.  However, as the metadata is aggregated in one place, the service provider has opportunities to enhance it and provide value-added services.

Static Repositories

OAI-PMH was designed as a lightweight protocol, but it does require some technical expertise to set up an OAI-compliant repository.  This presents a barrier to the small publishers that would benefit most from the disclosure.  

The static repositories model for using OAI-PMH is an alternative approach and lowers the technical barrier at the data provider end.  Instead of building an OAI-compliant repository, the data provider builds a ‘static repository’, effectively an XML file of the relevant metadata on a web-accessible server.  A separate static repository gateway between the data provider and the service provider handles the technical aspects of making the metadata available for harvesting, i.e. the complexity is shifted away from the data provider.  

This approach is useful where the data provider has small quantities of metadata (less than 5,000 records) that is not updated frequently (e.g. monthly or less).  It also depends on having a service provider to host a static repository gateway.

The Standard

The standard is developed and maintained by the Open Archives Initiative.  Specifications, guidelines for using it, tutorials, and a list of OAI-compliant tools can be found on the OAI web site.

OAI-PMH in the PALS Programmes

  • An OAI-compliant Metadata Repository for a Specialist Publisher of e-Journals  – EEVL helped Inderscience Publishers build an OAI-complaint repository for disclosing their journal metadata, and developed the TechXtra service for cross-searching metadata from many publishers.
  • STARGATE  – University of Strathclyde used the low tech static repositories approach to disclose metadata for four small library and information science journals.  A project extension allowed them to set up an experimental static repositories gateway for publishers and explore the feasibility of maintaining a permanent gateway.

Further Information

About OAI-PMH:  

About static repositories: