OpenAIRE entity identifier and PID mapping policy¶

(copied from https://docs.google.com/document/d/1PnvZpmhbanJu3AeOT-zdIyMKIHoGKC4_Z0UtDFDZAeM/edit#)

OpenAIRE assign internal identifiers for each object it collects.
By default, the internal identifier is generated as sourcePrefix::md5(localId) where

• sourcePrefix is a namespace prefix of 12 chars assigned to the data source at registration time
• localid is the identifier assigned to the object by the data source

After years of operation, we can say that:

• localId are unstable
• objects can disappear from sources
• PIDs provided by sources that are not PID agencies (authoritative sources for a specific type of PID) are often wrong (e.g. pre-print with the DOI of the published version, DOIs with typos)

Therefore, when the record is collected from an authoritative source:

• the identity of the record is forged using the PID, like pidTypePrefix::md5(lowercase(doi))
• the PID is added in a pid element of the data model.

When the record is collected from a source which is not authoritative for any type of PID:

• the identity of the record is forged as usual using the local identifier;
• the PID, if available, is added as @alternateIdentifier@s

As of November 2021, the following data sources are used as "PID authorities":

PID Type	Prefix (12 chars)	Authority
doi	doi_________	Crossref, Datacite, Zenodo
pmc	pmc_________	Europe PubMed Central, PubMed Central
pmid	pmid________	Europe PubMed Central, PubMed Central
arXiv	arXiv_______	arXiv.org e-Print Archive
handle	handle______	any repository

TODO: WHAT HAPPENS FOR RECORDS WITH BOTH pmc and pmid? pmc wins?

OpenAIRE also perform duplicate identification (see dedicated section for details).
All duplicates are "merged" together in a "representative record" which must be assigned to a dedicated OpenAIRE identifier (i.e. it cannot have the identifier of one of the aggregated record).
The following strategy is applied to generate the OpenAIRE identifier of a representative record, to ensure it is as stable as possible:

TODO