Metadata Harvesting with R and OAI-PMH

The Open Archives Initiative (http://www.openarchives.org/) develops and promotes interoperability standards that aim to facilitate the efficient dissemination of content. One key project is the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH, http: //www.openarchives.org/pmh/) which provides “a low-barrier mechanism for repository interoperability” for archives (institutional repositories) containing digital content (digital libraries). OAI-PMH allows people (service providers, such as the ones registered with the OAI listed on http://www.openarchives.org/service/listproviders.html) to harvest metadata (from data providers, such as the ones registered with and validated by the OAI listed on http: //www.openarchives.org/Register/BrowseSites/). Data Providers administer systems that support the OAI-PMH as a means of exposing metadata. Service Providers use metadata harvested via the OAI-PMH as a basis for building value-added services. OAI-PMH, currently in version 2.0, defines a mechanism for data providers to expose their metadata. The protocol mandates that individual archives map their metadata to the Dublin Core (DC, http://dublincore.org/), a simple and common metadata set for cross-domain information resource description. OAI-PMH is a set of six verbs or services that are invoked within HTTP, returning the request results in XML format. The OAI-PMH specification can be found at http:// www.openarchives.org/OAI/openarchivesprotocol.html. Here, we summarize the basic facts and terminology. 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. Repositories are network accessible servers that can process the six OAI-PMH requests, and are managed by a data provider to expose metadata to harvesters. OAI-PMH distinguishes between three distinct entities related to the metadata made accessible by the OAI-PMH: