The Open Citation Identifier (OCI) is a globally unique persistent identifier for bibliographic citations, created and maintained by OpenCitations, and this page provides a resolution service that takes an OCI and returns information about that citation. A formal description and definition of an OCI is given in:
Silvio Peroni, David Shotton (2019). Open Citation Identifier: Definition. Figshare. https://doi.org/10.6084/m9.figshare.7127816.
The search box above takes an OCI as input and returns metadata about the identified citation.
Each OCI has a simple structure: the lower-case letters oci
followed by a colon, followed by two numbers separated by a dash. For example, oci:06101801781-06180334099 is a valid OCI for citations defined within the OpenCitations Index.
The first number is the identifier for the citing bibliographic resource, while the second number is the identifier for the cited bibliographic resource. Each identifier is composed of two parts, a prefix that identifies the supplier database from which the citation is recorded, and a number is a unique identifier for a citing or cited entity within that database. Within the OpenCitations Index, all internal bibliographic resource identifiers are unique, and every citation recorded in the Index has an OCI. OCIs have also been created for open citations within other bibliographic databases where citing and cited works bear unique identifiers of the same type.
Each prefix is a short numerical string delimited by zeros that indicates the supplier database from which the citation is recorded, and in which the identifier is unique. For example, the prefixes starting with 06
followed by a sequence of 1-9
digits and then a final 0
are all OpenCitations prefixes, while 010
indicates that Wikidata is the supplier. Thus oci:01027931310-01022252312 represents a citation between two bibliographic resources (i.e. wd:Q27931310 and wd:Q22252312) whose metadata was in both cases supplied by Wikidata. Similarly, 020
indicates that Crossref is the source of the DOIs used to create the OCI. Thus oci:02001010806360107050663080702026306630509-02001010806360107050663080702026305630301 represents a citation between two bibliographic resources identified in Crossref by DOIs (i.e. http://dx.doi.org/10.1186/1756-8722-6-59 and http://dx.doi.org/10.1186/1756-8722-5-31), whose metadata can be retrieved in both cases by means of the Crossref API, if desired. In the Crossref example, the DOIs have been converted into purely numerical strings using a simple two-numeral look-up table, as explained in the OCI definition document.
A list of existing and actiive OCI bibliographic resource identifier prefixes and their meanings can be found in the following table.
| Prefix | Supplier | Identifier type | Example |
|---|---|---|---|
| 010 | Wikidata | Wikidata Identifier (QID) | oci:01027931310-01022252312 |
| 020 | Crossref | Digital Object Identifier (DOI) | oci:02001010806360107050663080702026306630509-02001010806360107050663080702026305630301 |
| 040 | Dryad | Digital Object Identifier (DOI) | oci:040050006013613273410133708070900-04003070302361019113701000000040801 |
| 06[1-9 digits]0 | OpenCitations | OpenCitations Meta Identifier (OMID) | oci:06101801781-06180334099 |