OAI stands for Open Archives Initiative. The point of OAI-PMH (OAI- Protocol for Meta-data Harvesting), created within the framework of this initiative, is
to provide a uniform standard for repositories sharing their meta-data. Repositories install an OAI server (a simple software) and upload their collected meta-data in accordance with the OAI standard. These OAI servers connect to the internet, thus external service providers (e.g. NDDA) can harvest always up to date meta-data.
