A database containing information about trusted repositories that are provided by the repository managers and are useful for human and machine users. It is a registry information system on which a register is maintained. These registries do not contain information about all metadata descriptions of digital objects, nor do they offer a list of PIDs of all stored digital objects. They do offer information based on standardized types on how to retrieve such information (e.g., the port under which OAI-PMH can be accessed to offer metadata). It is a set of files containing identifiers assigned to items with descriptions of the associated items. It is assignment of a permanent, unique and unambiguous identifier to an item.