This page provides information about the standards mentioned in this website, relevant to understand the data services provided.

Dublin Core
Short name for the Dublin Core Metadata Element Set (DCMES), also referred to as DC. Dublin Core was developed by the Dublin Core Metadata Initiative (DCMI) since 1995 to establish a cross-domain core set of metadata elements for simple and generic resource descriptions, and to facilitate interoperability. The set, consisting of 15 base elements, achieved wide application as part of the OAI-PMH protocol, and has been ratified by IETF (RFC 5013: 2007), ANSI NISO (ANSI / NISO Z39.85-2007) and ISO (ISO 15836: 2009).
Maintenance agency: Dublin Core Metadata Initiative (DCMI).

ISO 2709
ISO 2709 - Information and documentation -- Format for information exchange is the common format for exchange underlying all MARC (Machine Readable Cataloging) formats. It is a generalized format for communication, not for processing within systems. It consists of a record label, a directory, data fields, and field and record separators.
The current version is ISO 2709 : 2008.

Linked data
Linked data is data on the Web available in a standard format (e.g. RDF/XML, RDF Turtle), reachable and manageable by Semantic Web tools, providing not only access but also relationships among data thus making datasets interrelated. The source data can be produced with semantic web technologies (RDF, OWL, SKOS, etc.) or be converted from existing databases. Linked data makes it possible to access and reuse data from multiple sources at once and combine it without the need for a single common schema that all data shares. Basic requirements of linked data are the use of URIs as names for concepts or objects, use of HTTP URIs to access them, provide useful metadata about them using RDF standards, and include links to other related URIs, so to enrich data and to enhance discoverability.
For an introduction and to know more about linked data standards see W3C website, here.
For the linked datasets provided by NLP, see documentation on LOD at the European Library - Data Model and LOD at the European Library – General Information.

MARCXchange is the short name of ISO 25577:2013 - Information and documentation – MarcXchange. The standard specifies the requirements for a generalized XML-based exchange format for bibliographic records as well as other types of metadata. It consists of an XML-based alternative for ISO 2709 such that any existing format based on ISO 2709 could be represented.
The standard is available here. A draft text of the standard is available here.


Metadata Object Description Schema (MODS) is a schema for a bibliographic element set that may be used for a variety of purposes, and particularly for library applications. Established by the Library of Congress in 2002, MODS is an XML schema intended to carry selected data from existing MARC 21 records as well as to enable the creation of original resource description records. It includes a subset of MARC fields and uses language-based tags rather than numeric ones, in some cases regrouping elements from the MARC 21 bibliographic format. Current version is 3.6 (May 2015).
Maintenance agency: The Library of Congress, Network Development and MARC Standards Office.

OAI-PMH - Open Archives Initiative - Protocol for Metadata Harvesting specifies a mechanism for harvesting records containing metadata from repositories. It provides a simple option for data providers to make their metadata available to services, based on the open standards HTTP and XML. The exposed metadata may be in any format agreed by a community although unqualified Dublin Core is specified to provide a basic level of interoperability. With OAI-PMH metadata from many sources can be gathered and services can be provided based on this aggregated data. OAI-PMH current version is 2.0 (June 2002).
Maintenance agency: Open Archives Initiative.

PURL - Persistent Uniform Resource Locator is a type of Web address that acts as permanent identifier in the face of a dynamic and changing Web infrastructure. The concept was developed at OCLC in the 90s. Instead of resolving directly to Web resources, PURLs provide a level of indirection that allows the underlying Web addresses of resources to change over time without negatively affecting systems that depend on them. This capability provides continuity of references to network resources that may migrate from machine to machine for business, social or technical reasons.
Official website.

The Resource Description Framework (RDF) is a language for representing information about resources in the World Wide Web, particularly intended for representing metadata to be processed by applications. RDF is based on the idea of identifying things using Web identifiers (called Uniform Resource Identifiers, or URIs), and describing resources in terms of simple properties and property values, so that information can be exchanged between applications without loss of meaning. RDF comprises a set of specifications developed and endorsed as Recommendations by the W3C.
See current status of the RDF specifications here.

RDF Turtle
RDF Turtle (Terse RDF Triple Language), is a recommendation of the W3C specifying a concrete syntax for the representations of RDF graphs, in a compact and natural text form, with abbreviations for common usage patterns and datatypes.
The specification is available here.

Research Information Systems (RIS) is a format for bibliographic references that enables users to capture and import such references from bibliographic information systems (such as library catalogues, Google Scholar, Web of Science, etc.) to their personal reference managers (such as EndNote, Reference Manager, etc.). The format consists of a plain text file with standard tagged fields.
See the complete specification here.

UNIMARC (standing for Universal MARC) is a specific implementation of ISO 2709, defining the content designators (field tags, indicators and subfield codes), and the content values of coded data fields, to be assigned to bibliographic records in machine readable form and to specify the logical and physical format of the records. Intended to be a carrier format for exchange purposes, it does not stipulate the form, content or record structure within individual systems. Being initially designed, in the 70s, as an interchange format to facilitate conversion to and from different MARC formats, UNIMARC became also a standards for the production of original records and evolved to a suite of specifications encompassing bibliographic, authority and holdings records. UNIMARC standards were developed and are maintained by IFLA – International Federation of Library Associations and Institutions. The maintenance body is the Permanent UNIMARC Committee, working within the IFLA UNIMARC Strategic Programme, since 2003 chaired by the National Library of Portugal.
Information about UNIMARC documentation is available here.

URN - Uniform Resource Name has been used historically to refer to both URIs (Uniform Resource Identifiers) under the "urn" scheme (RFC2141) which are required to remain globally unique and persistent even when the resource ceases to exist or becomes unavailable, and to any other URI (RFC3986) with the properties of a name. URN-based services in the NLP data services are used to retrieve data by unique identifiers such as ISBN, record ID number, legal deposit number, etc.


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