Persistent Identifiers (PIDs)

Digital objects in HELIPORT are identified by globally unique persistent identifiers (PIDs). They are stored in heliport.core.models.DigitalObjectIdentifier. The method heliport.core.models.DigitalObject.preferred_identifier() can be used to find an appropriate identifier for an object.

Note

In the past, persistent identifiers were stored in digital objects’ persistent_id and generated_persistent_id attributes. These fields are deprecated.

heliport.core.models.DigitalObjectIdentifier can store identifiers for different aspects of a digital object. Currently, the model supports main identifiers which represent the digital object itself, and identifiers for metadata graphs. The latter can be used in the future as graph names in a graph database, or to implement a multi-layered “FAIR Digital Objects” approach. Other aspects may be added in the future.

PIDs can also be differentiated by their “scheme”. This attribute combines the notion of a “PID provider” (think DOI or Handle.net) with information about how to display the PID to the user, and which HELIPORT-internal implementation to use to make changes to this PID at the provider site.

PID Generation

HELIPORT uses post-save hooks to automatically generate, or mint, identifiers for a digital object, when it is first saved.

For all digital objects, an associated “HELIPORT ID” will be created, which is a fallback identifier that can be used if the object has no other identifiers. The HELIPORT ID is equal to the landing page URL of the digital object.

HELIPORT also supports minting Handle.net identifiers, or “handles”. If Handle.net integration is set up correctly, these are created in addition to the HELIPORT ID. Handles consist of a fixed prefix which you acquire through the CNRI, and a suffix which is unique to each minted handle. All handles can be resolved via the resolver URL https://hdl.handle.net/<handle> which redirects to the landing page of the associated digital object.

HELIPORT chooses the handle suffix based on the namespace associated with the digital object, and its primary key. heliport.core.models.DigitalObject.suffix_for_pid_generation() provides a string which is used for this purpose.

More information can be found in heliport.core.pid_registration.

External Identifiers

HELIPORT can also use external identifiers, i.e., identifiers which were not generated by HELIPORT, to refer to digital objects. Typically, these will be entered by the user or imported from an external system or database. Possible examples are DOIs of publications (issued by DataCite or Crossref), IGSNs for physical samples, or URLs for ontology terms.

To associate an external identifier with a digital object, heliport.core.models.DigitalObject.set_identifier() can be used. If this method is called before saving the object for the first time, no other identifiers will be created for this digital object.

heliport.core.models.DigitalObject.set_identifier() determines which identifier was passed based on the DataCite Ontology. The implementation can be found in heliport.core.utils.identifiers.