Crossref began its service by linking publications to other publications via references. Today, this extends to relationships with associated entities. People (authors, reviewers, editors, other collaborators), funders, and research affiliations are important players in this story. Other metadata also figure prominently in it as well: references, licenses and access indicators, publication history (updates, revisions, corrections, retractions, publication dates), clinical trial and study information, etc. The list goes on.
This is a companion discussion topic for the original entry at https://www.crossref.org/blog/the-article-nexus-linking-publications-to-associated-research-outputs/