Have you noticed the alphanumeric string that appears after the letters “doi” in full-text Medline articles? That string is a Digital Object Identifier (DOI). It contains descriptive information and a permanent link to an electronic document or object, unlike a URL that may change over time.
The system is managed by the International DOI Foundation, an open membership consortium that includes both commercial and non-commercial partners and is implemented by Registration Agencies (RAs). The RAs allocate DOI® name prefixes, register DOI names and provide the necessary infrastructure for quality assurance.