It seems a strange thing to take an interest in, but for readers of journals, DOIs (digital object identifiers) are commonplace, and understanding how the heaving virtual library is organised can be useful in all sorts of ways.

I stumbled upon an (arguably) interesting blog post, DOIs unambiguously and persistently identify published, trustworthy, citable online scholarly literature. Right? » via PLOS Blogs, Research findings: going deeper than the article.

CrossRef is a DOI registration agency, though there are actually 8 such agencies, and DOIs hold no information on which was used to create them. This leads to some inconsistencies in their compatibility with the web services called “APIs” (application programming interfaces), which provide standardised means to access information on content at a DOI 'address'. For example,

The South Park movie has a DOI:

http://dx.doi.org/10.5240/B1FA-0EEC-C316-3316-3A73-L

This following two DOIs point to the same article- there is no apparent difference between the two copies:

http://dx.doi.org/10.6084/m9.figshare.91541

http://dx.doi.org/10.1038/npre.2012.7151.1

These journals assigned DOIs, but not through CrossRef:

http://dx.doi.org/10.3233/BIR-2008-0496

http://dx.doi.org/10.6084/m9.figshare.95564

http://dx.doi.org/10.3205/cto000081

To search metadata for the above examples, you need to visit four sites:

http://search.crossref.org

https://ui.eidr.org/search

https://www.medra.org/en/search.htm

http://search.datacite.org/ui

The truth is, the DOI has nothing specifically to do with citation or scholarly publishing. It is simply an identifier that can be used for virtually any application.

One of the more common companions to CrossRef (a not-for-profit body representing commercial publishers) is DataCite (comprising public research organisations, plus Microsoft Research), who assign DOIs for the up and coming data repository figshare.

See also ✖ Fundref - CrossRef's provided means to access funding information related to scholarly content

✖ CrossCheck - used by many universities (on iThenticate) to check for plagiarism in essays etc. (Turnitin). Presentation slides from the neuroscientist who created Turnitin describe how it works with CrossCheck here.

✖ CrossMark - informs readers of changes to content in a publication, including within a pdf file. A video explaining it is available at CrossRef's site (below), plus some of their conference slides on SlideShare.