Persistent Identifiers

In an environment of increasingly widespread data sharing and reuse, requirements for its unique identification and permanent access are essential for both digital preservation and semantic web exploitation, in particular in the field of linked data.

IDENTIFIERS FOR METADATA RECORDS

BNP has implemented a system of persistent identifiers for metadata records contained in its different information systems, consisting of two components. The first is a unique identifier for each data record that also identifies the data provenance through a namespace. The second component is a service that permanently locates the metadata record on the network, regardless of application / location changes, ensuring that the identifier always resolves to the correct address where the data is currently located.

Furthermore, with this system of identifiers used as persistent URLs, one gets clearer and more concise web addresses than the URLs generated by software applications, usually composed dynamically by the various data elements that make up a search query.

Namespace and identifier composition

The implemented namespace root is http://id.bnportugal.gov.pt

• Resource type (record type, bibliographic {bib} or authority {aut})
• Data source, designating the system to which the record belongs:
• BNP Catalog {catbnp}
• Portuguese National Bibliography {bibnacional}
• PORBASE Collective Catalog {porbase}
• National Register of Digital Objects {rnod}
• Unique identifier within the data source (the record number in the source database)

Therefore, the identifier syntax is as follows:
http://id.bnportugal.gov.pt/{type-of-record}/{data-source}/{id}

Identifier for the authority record 1047133 in the BNP Catalogue
http://id.bnportugal.gov.pt/aut/catbnp/1047133

Identifier for the bibliographic record 2026159 in the Portuguese National Bibliography
http://id.bnportugal.gov.pt/bib/bibnacional/2026159
corresponding, in the respective online service, to the URL
http://bibliografia.bnportugal.gov.pt/bnp/bnp.exe/registo?2026159

Persistent identifiers are implemented in field 003 (Persistent Identifier) of the UNIMARC bibliographic records of the following information systems: BNP Catalogue, PORBASE Union Catalog, RNOD - National Register of Digital Objects e Portuguese National Bibliography. They are also implemented in field 003 of the UNIMARC authority records of the BNP Catalogue. In these systems a feature was also implemented to enable view and copy of the persistent URL of each record when displayed. All datasets available on this Open Data Portal have been updated accordingly.

IDENTIFIERS FOR DIGITAL RESOURCES

The resources available in the National Digital Library (BND) have persistent identifiers under the Persistent Uniform Resource Locator (PURL) system.

Identifiers for the component parts of a resource

Persistent identifiers are provided for each of the component parts of a resource, where applicable (pages of a single item or volume resource; and volumes and pages of resources with two or more items or volumes), using the following syntax: