Global overview of open cultural data 

Cultural data include information about objects, publications, pictures or music collections created and distributed by institutions from cultural and artistic sector. Given the great value of this cultural heritage, the European Union, through the Directive 2013/37/EU -and transposed into national legislation through Law 18/2015- has modified the scope of the application of the re-use of public sector information including European libraries, museums and archives.

Nevertheless, opening up this information is a big challenge because it is essential to transform different types of content together with their metadata (title, materials, dates, locations, authors...), into reusable formats and make them available under an open license. For these reasons, open cultural data is still a young movement which has a long way to go to reach other sectors which have been early open data adopters.

Despite of the barriers, opening up cultural resources provides several benefits. Firstly, the openness of the collections would increase the access, visibility and usage of the heritage. Moreover, this would stimulate collaboration among institutions worldwide,  promoting the creation of new services and supporting the creative re-use of materials.

One of the first steps towards open cultural data was The Commons project, an international initiative to share world's public photography archives, licensed with “no known copyright restrictions”. In 2008, Sydney’s Powerhouse Museum became the first museum to join the project, which, one year later, released its collection metadata under a Creative Commons CC-BY-SA license.

In 2011, the British Museum launched a linked data service and a more open licence for access to its collections while the European digital library Europeana launched an API providing access to over 40 million objects from 1500 museums, libraries, archives and audio-visual collections aggregated from across Europe. Besides, apart from its own open data portal, this platform has a section where tools, real applications and case studies of re-use of open cultural data are regularly published.

Currently, one of the international museums leading the openness of cultural information is the SMK Danish center in which approximately 25,000 images of artworks on its website are in the public domain; free to use for any commercial, academic or scientific purpose without asking permission from the SMK or anyone else.

At national level, two remarkable examples of the Spanish commitment to the openness of cultural data are the National Library of Spain which has its own PSI plan and open data portal, and the Biblioteca Virtual Miguel de Cervantes which contains about 200,000 records, produced and stored in RDF format making the items interoperable. Digital resources produced by this institution are assigned permanent identifiers that enable the creation of persistent links.

Internet has been an opportunity for these entities to target larger audiences, allowing users to enjoy, contribute, participate and share the artistic heritage. In order to help cultural institutions on their journey towards openness, OpenGLAM was launched, an initiative run by Open Knowledge that promotes free and open access to digital cultural heritage held by galleries, libraries, archives and museums; fulfilling five principles:

1. Release digital information about the artefacts (metadata) into the public domain using an appropriate legal tool such as the Creative Commons Zero Waiver. 

 2. Keep digital representations of works for which copyright has expired in the public domain by not adding new rights to them.

3. Explicit statement of your wishes and expectations with respect to reuse and repurposing of the descriptions, the whole data collection, and subsets of the collection.

4. When publishing data use open file formats which are machine-readable.

5. Opportunities to engage audiences in novel ways on the web should be pursued.

More and more cultural institutions are committed to publishing their digital content under open license and creating APIs that allow programmers to work with their information. Nevertheless, this sector still needs to keep working to make accessible the large volume of stored data; which would be a new success for the international open data community that wishes the openness of the information regardless of its origin.