CrossRef

CrossRef is on of the DOI registration agencies, responsible for scholarly and professional publications; with more than 2000 publishers participating. The participating publishers register metadata records for each DOI and thereby built a big multidisciplinary reference database with more than 29 million records.

The most usage scenarios described below require that the institution become an CrossRef affiliate, e.g. by signing the
 * library agreement, see http://www.crossref.org/03libraries/index.html Conditions: There is no charge for most libraries to get a CrossRef account to retrieve DOIs or metadata, but there is a fee for high-volume downloads (more than 1 million requests per year)
 * affiliate agreement, see http://www.crossref.org/04intermediaries/index.html Conditions: annual fee according to price list.

The MPG is a CrossRef affiliate, a program which focuses on "organizations that are not primary publishers but want to retrieve CrossRef DOIs (Digital Object Identifiers) and bibliographic metadata for persistent linking to publisher full text", s. http://www.crossref.org/04intermediaries/index.html. Further information is available from Inga.

Fetching Metadata
CrossRef supports several methods to request the metadata from its reference database:

via the OpenURL interface
The OpenURL interface provides an convenient way to access the metadata record for a known DOI. The service supports requests in compliance with version 0.1 or version 1.0 of the OpenURL standard. Currently no user account is required to access this interface, but this is subject to change.

Example requests:
 * article, crossref_query output: http://www.crossref.org/openurl?url_ver=Z39.88-2004&req_dat=usr:pwd&rft_id=info:doi/10.1103/PhysRev.47.777&redirect=false
 * article, unixref output: http://www.crossref.org/openurl?url_ver=Z39.88-2004&req_dat=usr:pwd&rft_id=info:doi/10.1103/PhysRev.47.777&format=unixref&redirect=false
 * book chapter, crossref_query output: http://www.crossref.org/openurl?url_ver=Z39.88-2004&req_dat=usr:pwd&rft_id=info:doi/10.1007%2F978-3-540-73859-6_29&redirect=false
 * book chapter, unixref output: http://www.crossref.org/openurl?url_ver=Z39.88-2004&req_dat=usr:pwd&rft_id=info:doi/10.1007%2F978-3-540-73859-6_29&format=unixref&redirect=false

More information: http://www.crossref.org/openurl_info.html

via the OAI interface
CrossRef operates an OAI-PMH service provider for distributing metadata to subscribers which is especially helpful for a bulk download of metadata records. Accessing this interface requires an additional agreement which is currently not available in the MPG.

Example requests:
 * Identify: http://oai.crossref.org/OAIHandler/?verb=Identify
 * Record (login required): http://oai.crossref.org/OAIHandler/?verb=GetRecord&metadataPrefix=cr_unixml&identifier=info:doi/10.1038/42304

More information: http://www.crossref.org/webservices.html

Available Outputs

 * crossref_query output: includes a minimal set of metadata to describe a reference, e.g. only the first author. Schema: http://www.crossref.org/qrschema/crossref_query_output2.0.xsd
 * unixref output: a more verbose XML response, e.g. complete author information. Schema: http://www.crossref.org/schema/unixref1.0.xsd

Additional Tools
doi resolver (provide a doi and be redirected to the corresponding article location): http://dx.doi.org

free doi lookup (provide metadata and receive the corresponding doi): http://www.crossref.org/guestquery/

simple text query (provide a reference and retrieve doi): http://www.crossref.org/SimpleTextQuery/ Example reference: ''A. Bergstrom, C.C. Hsieh, P. Lindblad, C.M. Lu, N.R. Cook and A. Wolk, Obesity and renal cell cancer — a quantitative review, Br. J. Cancer 85 (2001), pp. 984–990.''