Interoperability refers to the ability of different systems to communicate and share information and services. In a general sense, interoperability is an important feature for digital libraries because it allows for the sharing of a collection's information regardless of the hardware, platform, or applications used.
Interoperability is achieved through the implementation of standardized protocols. One common protocol example is the HyperText Transfer Protocol (HTTP) that allows computers to request resources from other computers. Another example of a protocol that is important for institutional repositories is the Open Archives Initiative - Protocol for Metadata Harvesting (OAI-PMH).
OAI-PMH was created by the Open Archives Initiative (OAI) to provide an "application-independent interoperability framework" (OAI-PMH v.2, 2004) based on a model of data providers and service providers. Data providers use the OAI-PMH to expose and describe metadata about their repositories while service providers use the OAI-PMH to gather or "harvest" this metadata and create additional services.
This model provides many benefits for institutional repositories. The hierarchical nature of this model provides a simple method for making repositories scaleable. The ability to interact with multiple data providers allows service providers to aggregate across multiple collections. Dividing services across multiple machines provides a mechanism for performing load balancing. By controlling the information chosen in the aggregation process, repositories can also help define collection boundaries to support the building of specific communities or domains. Finally, by creating a single access point across multiple collections and adding services, this model can aid in information discovery.
Nelson, M. (2004). A review of institutional repository projects and technologies. Humanities
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OAI-PMH v.2, (rev. 2004). The Open Archives Initiative protocol for metadata harvesting. Retrieved 06/28/2005 from http://www.openarchives.org/OAI/openarchivesprotocol.html