Metadata Harvesting refers to gathering metadata from multiple places or archives and storing it in a central database.
Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) is a low-barrier mechanism for repository interoperability. Data Providers are repositories that expose structured metadata via OAI-PMH. Service Providers then make OAI-PMH service requests to harvest that metadata. OAI-PMH is a set of six verbs or services that are invoked within HTTP. It is developed by Open Archives Initiative (OAI).
An implementation of OAI-PMH requires metadata to be encoded in simple Dublin Core (DC) format for interoperability in general. Additional metadata standards may also be supported such as Qualified DC.
In the open network environment, to increase data interoperability between different systems, these aspects need to be carefully considered by metadata working groups and librarians such as principles in making metadata standards, mapping between various metadata standards and search and retrieval protocols.