This is a bare bones selection of points from the OAI tutorial. All dot and numbered points are taken from this tutorial.
- Open Archive Initiative (OAI)
OAI is an initiative to develop and promote interoperability standards . . . .
- OAI Protocol for Metadata Harvesting (OAI-PMH)
OAI-PMH is a lightweight harvesting protocol for sharing metadata between services.
In the OAI context, harvesting refers specifically to the gathering together of metadata from a number of distributed repositories into a combined data store.
- Data Provider
A Data Provider maintains one or more repositories (web servers) that support the OAI-PMH as a means of exposing metadata.
- Service Provider
A Service Provider issues OAI-PMH requests to data providers and uses the metadata as a basis for building value-added services.
Thus repositories are essentially data providers — if they support OAI-PMH.
More from here:
Main ideas of OAI
- world-wide consolidation of scholarly archives
- 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)
- Data Providers (open archives, repositories) provide free access to metadata, and may, but do not necessarily, offer free access to full texts or other resources. OAI-PMH provides an easy to implement, low barrier solution for Data Providers.
- Service Providers use the OAI interfaces of the Data Providers to harvest and store metadata. Note that this means that there are no live search requests to the Data Providers; rather, services are based on the harvested data via OAI-PMH. Service Providers may select certain subsets from Data Providers (e.g., by set hierarchy or date stamp). Service Providers offer (value-added) services on the basis of the metadata harvested, and they may enrich the harvested metadata in order to do so.
How it works
The Service Provider (Harvester) sends out requests to the repository data provider. The requests are sent in the common web HTTP language (so no firewall problems) in the form of 6 “verbs”:
“The Service Provider is not required to use all types. However a repository must implement all types.”
The Data Provider (Repository) responds in XML syntax with the following Responses:
- General information
- Metadata formats
- Set structure
- Record identifier
- OAI-PMH supports any metadata format encoded in XML.
- Dublin Core is the minimal format specified for basic interoperability. (So Dublin Core is expressed in XML syntax.)
- Repositories must be able to disseminate unqualified Dublin Core.
- Further arbitrary metadata formats can be defined and transported via the OAI-PMH. (In XML format.)
- Any returned metadata must comply with an XML namespace specification.
- The Dublin Core Metadata Element Set contains 15 elements. All elements are optional, and all elements may be repeated.