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Posted on Monday August 14, 2017

Updated on Monday November 6, 2023

Linked Open Data

Linked Open Data is a way of publishing structured data that allows metadata to be connected and enriched, so that different representations of the same content can be found, and links made between related resources. 

You see Europeana's motivation for using Linked Open Data (LOD) in the animation below.

This page first starts by providing non-technical information about Europeana and linked data, which is suitable for readers of all backgrounds. It then provides a technical overview about how Europeana's Linked Data is structured, which is aimed at those with detailed knowledge of linked data, and  references for additional technical details.

If you have any questions or feedback, contact us directly via api@europeana.eu.

Current status

Linked Open Data at Europeana started as an experimental pilot in February 2012, when a small number of data providers committed at an early stage to Europeana's initiative of promoting more open data. The pilot was described in a paper presented at the Dublin Core 2011 conference. In October 2012, a large subset of Europeana’s dataset (metadata on 20 million texts, images, videos and sounds) was transformed into linked data and made available from data.europeana.eu (the domain name data.europeana.eu is the corresponding domain of www.europeana.eu in the web of linked data, as explained in the technical details). Within the Europeana Creative project, a new pilot was developed and hosted by Ontotext. containing the full Europeana dataset at the time (metadata on about 36 million objects).

The metadata for all the objects in the Europeana website is open, in that it is all licensed under the CC0 Public Domain Dedication under the terms of the Data Exchange Agreement (DEA), and can be freely downloaded in bulk, harvested via the OAI-PMH Service, and accessed via the Record API and the SPARQL endpoint.

The data is represented in the Europeana Data Model (EDM). The described resources are each addressable and dereferenceable by their URIs; for instance, https://www.europeana.eu/en/item/90402/SK_C_5 leads either to an HTML page on the Europeana website for the object it identifies or to raw, machine-processable data on this object. data.europeana.eu includes semantic connections to external (linked data) sources. These links come mostly from semantic enrichment connecting Europeana items to places, concepts, persons and time periods. But the number of external links provided by data providers is constantly growing including links to AAT, GND, Iconclass, VIAF) or any domain vocabulary following the EDM recommendations for metadata on contextual resources (see the list of vocabularies supported by Europeana).

Tools created with the Europeana Linked Open Data

Some tools have been created, which make use of Europeana LOD. Below are some of the earliest cases, and in posts on the topic other examples can be found.

ECLAP Linked Open Graph

ECLAP Linked Open Graph

ECLAP Linked Open Graph allows users to see, explore and browse the relationships among the ECLAP content and other types of resource created on the ECLAP platform.

Data structure

This section provides information on how the metadata served by data.europeana.eu is organised. We assume that the reader has extensive knowledge of Linked Data technology. Note also that the data.europeana.eu URIs mentioned in this section are content negotiated, and when clicked in a web browser they will lead to the Europeana website and not to the actual RDF data. To access the RDF content, the HTTP Accept header must be used, as explained in the already referenced technical details on content negotiation.

Background - The Europeana Data Model (EDM)

The Europeana Data Model offers the opportunity to attach every statement to the specific resource it applies to, and to reflect some basic form of data provenance. The main EDM requirements include:

  • distinguishing between a 'provided item' (painting, book) and its digital representations

  • distinguishing between an item and the metadata record describing it

  • allowing the ingestion of multiple records for the same item, which may contain contradictory statements about it

As a consequence of EDM having to meet these requirements, EDM data has a level of complexity that is comparable to the data of many Europeana providers, and thus, we argue, enables better exploitation of that data than simpler formats like Europeana's own earlier Europeana Semantic Elements (ESE). Note also that, as much as possible, EDM re-uses elements coming from already-established vocabularies, such as Dublin Core, OAI-ORE, SKOS and CIDOC-CRM, thus lowering the cost of its creation and, hopefully, supporting its adoption.

For more information on EDM, we refer to the EDM Definitions and EDM Primer on Europeana's technical documents page. The EDM OWL ontology is accessible through content negotiation but it is also directly downloadable as an OWL file. Please be aware that both data.europeana.eu and those documents are under constant revision. There could therefore be some discrepancies between them!

A walk through the resources served at data.europeana.eu

The core EDM classes, together with the properties we expect to be applied to their instances, are presented in these templates (NB: of course not all EDM properties are used for every object exposed in Europeana). The EDM data harvested from Europeana providers, as well as the enrichment work by Europeana, allow us to create and describe a network of EDM resources for every Europeana object, as described in the EDM Primer. The following explains in more detail the data that can be found for every class of resource served by data.europeana.eu:

Item (Provided Cultural Heritage Object): Item resources represent objects (painting, book, etc.) for which institutions provide digital representations to be accessed through Europeana. Provided Cultural Heritage Object  URIs (e.g. http://data.europeana.eu/item/...) are the main entry points in data.europeana.eu. A provided cultural heritage object is the hub of the network of relevant resources (see below). When applicable, the Europeana URIs for these objects also link, via 'owl:sameAs' statements, to other linked data resources about the same object. In data.europeana.eu, no descriptive metadata (creator, subject, etc.) is directly attached to item URIs. It is instead attached to the proxies that represent a view of the object, from a specific institution's perspective (either a Europeana provider or Europeana itself).

Title:
Example of a Provided Cultural Heritage Object. (the Cittie of London 31, The British Library)
Example of a Provided Cultural Heritage Object.
(the Cittie of London 31, The British Library, http://www.europeana.eu/en/item/2059209/item_92037__http___www_bl_uk_onlinegallery_onlineex_crace_t_zoomify87870_html)

Provider's proxy: These resources (e.g. http://data.europeana.eu/proxy...) are used as subjects of descriptive statements (creator, subject, date of creation, etc.) for the item, which are contributed by a Europeana provider. In the OAI-ORE model, proxies enable the separation of different views for the same resource, in the context of different aggregations. This allows us to distinguish the original metadata for the object from the metadata that is created by Europeana, an important requirement for us. Descriptive properties that apply to these proxies mostly come from Dublin Core : view an example. Proxies are connected to the item they represent a facet of using the 'ore:proxyFor' property. They are attached to the aggregation that contextualises them using 'ore:proxyIn'. Note to the reader: given the lack of support for named graphs (aka 'quadruples') in the RDF standard, ORE introduced proxies in order to support referencing resources in the context of a graph. Eventually, named graphs may be supported by Europeana, which could lead to obsolescence of the proxy construct.

Providers Proxy
Descriptive statements for an item contributed by a Europeana provider being displayed in the Europeana website. (source: http://www.europeana.eu/en/item/2059209/item_92037__http___www_bl_uk_onlinegallery_onlineex_crace_t_zoomify87870_html ; note: the screenshot was taken from a previous version of the Europeana website).

Provider's aggregation: These resources (e.g. http://data.europeana.eu/aggre...)  supply data related to a Europeana provider's gathering of digitised representations and descriptive metadata for an item. As shown in this example, the data are related to digital resources about the item, be they files directly representing it ('edm:object' and 'edm:isShownBy') or webpages showing the object in context ('edm:isShownAt'). These resources may also provide controlled rights information applying to these resources ('edm:rights'). Other statements provided in the record as the descriptive metadata for the item, but that do not always clearly apply to the item, are also attached to aggregations. Finally, provenance data is given in statements using 'edm:provider' (the organisation who delivers data directly to Europeana) or 'edm:dataProvider' (the organisation who contributes data indirectly to Europeana). The aggregation is connected to the item resource using the 'edm:aggregatedCHO' property.

Providers Aggregation
Statements of the provider’s aggregation being displayed in the Europeana website. Provenance information is highlighted at the bottom of the screen, and information about rights and the digital representation is highlighted in the top right corner. (sources: http://www.europeana.eu/en/item/2059209/item_92037__http___www_bl_uk_onlinegallery_onlineex_crace_t_zoomify87870_html and https://www.webarchive.org.uk/wayback/en/archive/20190626074633/http://www.bl.uk/onlinegallery/onlineex/crace/t/largeimage87870.html ; note: these screenshots were taken from a previous version of these websites).

Europeana's proxy: The second type of proxies served at data.europeana.eu. are Europeana proxies (e.g. http://data.europeana.eu/proxy...) which provide access to the metadata created by Europeana for a given item, distinct from the metadata provided by the provider. Here one can find administrative metadata (e.g., the date of publication at Europeana, the Europeana dataset the item belongs to) and 'edm:year' statements, indicating a normalised date associated with the object. The semantic enrichment made by Europeana results in properties of the Europeana proxies that link to external resources. Finally, a proxy is connected to the item it represents a facet of, using the 'ore:proxyFor' property, as well as to the aggregation that contextualises it, using 'ore:proxyIn'.

Europeana Proxy
Statements of the Europeana’s proxy being displayed in the Europeana website. Administrative information is highlighted in the middle of the screen, and the section with the semantic enrichment is highlighted in the bottom. (source: http://www.europeana.eu/en/item/2059209/item_92037__http___www_bl_uk_onlinegallery_onlineex_crace_t_zoomify87870_html ; note: the screenshot was taken from a previous version of the Europeana website).

Europeana's aggregation: a Europeana aggregation (e.g. http://data.europeana.eu/aggre...) bundles together the result of all data creation and aggregation efforts for a given item. It aggregates the provider's aggregation (using ore:aggregates), which in turn will connect to the provider's proxy. Next to the provider aggregation, one can find the digitised resources Europeana.eu serves for the item, i.e., an object page ('edm:landingPage') and a thumbnail ('edm:preview'). The Europeana proxy is also connected to this aggregation, as mentioned above.

Europeana Aggregation

Statements of the Europeana’s aggregation in use at the Europeana website. The highlights show the edm:landingPage in the address bar of the browser, and the image previewing the digital object in the top of the screen. (source: http://www.europeana.eu/en/item/2059209/item_92037__http___www_bl_uk_onlinegallery_onlineex_crace_t_zoomify87870_html ; note: the screenshot was taken from a previous version of the Europeana website).

Namespaces used in data.europeana.eu

The following RDF namespace abbreviations are currently used in data.europeana.eu:

Further Reading

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