The Archives Hub provides interfaces that are accessible in a machine-to-machine way, enabling systems to access the descriptions and retrieve the data.
Search/Retrieve via URL is a search protocol to query Internet indexes or databases and return search results, specifying the syntax for both the search queries and the search results. SRU defines a standard form for Internet search queries as well as the structure of the responses, enabling Internet databases to be queried more seamlessly, without the need of more expensive and complicated meta-search protocols. The Archives Hub uses SRU internally, as well as providing an external SRU interface.
The Open Archives Initiative Protocol for Metadata Harvesting is a simple protocol that allows services (such as the Hub) to expose metadata for harvesting. This means that other services can regularly gather metadata.
OAI-PMH is a metadata harvester that locates and aggregates metadata from different data sets. A metadata harvester can be used to integrate data from a number of sources into one catalogue; users can then search the OPAC, locate the metadata within the catalogue and be linked to the content at the original repository’s site. OAI allows multiple forms of metadata to be exposed but mandates DC as a minimum. Many data providers do not provide richer metadata formats. Only the metadata needs to be stored locally and not the files themselves.
OAI-PMH is based on common standards: HTTP and XML. It is intended as a low-barrier solution, but a level of manual intervention in harvesting metadata is required and incremental harvesting may be problematic. There is a high level of flexibility in the protocol and in Dublin Core, which can create obstacles for service providers.
Z39.50 is a client-server protocol for search and retrieval of data from remote databases. It specifies procedures and formats for a client to search a database provided by a server, retrieve records and perform other information retrieval functions such as sort and browse.
The XML file containing the locations of Hub contributors is available for download.