OAI-PMH is an XML based protocol for metadata exchange using HTTP as the transport layer. An OAI-PMH system consists of two parts, a repository on the one and the harvester on the other end. The repository is an HTTP accessible server that exposes metadata to its client, the harvester. A repository is required to deliver metadata following the DublinCore element set version 1.1 metadata scheme. Additionally it may deliver metadata in any arbitrary format, that can be encoded as XML.

For a more detailed introduction please see the OAI-PMH specification.

Metadata Prefixes

The Opencast OAI-PMH server supports three metadata prefixes:

Prefix Description
oai_dc Dublin core element set 1.1 as required by the OAI-PMH specification
matterhorn Opencast media package representation
matterhorn-inlined Opencast media package representation with embedded catalogs

Note that the metadata prefix oai_dc is a standard metadata representation supported by all OAI-PMH servers and harverster, while the other prefixes are specific to Opencast. If you use an harvester in your third-party application, the havester will therefore need to be extended to support the Opencast-specific metadata prefixes.


Term Description
Repository An entity that holds a set of items to be disseminated via the OAI-PMH protocol. Different repositories may hold different sets of items.
Channel The client's perspective on a repository. Each channel is backed by a single repository (1:1 relationship) so these terms may be used synonymously depending on the perspective.
Item The base entity of a repository. In Opencast an item is equal to a mediapackage.
Metadata format OAI-PMH repositories disseminate their content in various formats. The oai_dc format is mandatory to each OAI-PMH repository. Formats are expressed in XML.
Metadata prefix The prefix identifies a metadata format. The terms are often used synonymously.