It is time to introduce the unifying concept of metadata, this being structured and controlled descriptions of a body of data or of a narrative and including simple components such as authorship, article titles, abstracts, aYiliations and provenance and publication dates. These formal structures now allow metadata to be more easily processed and analysed using AI/ML methods and provide infrastructures for obtaining for example metrics relating to research impacts. Whereas the commercial models that many publishers used in the past in the era before open-access would result in access to the digital journal article itself being paywall-protected in some manner, the metadata associated with that article was not so protected and was made readily available for use by anyone. In 2000, the Crossref organisation 7 was set up by a consortium of publishers, libraries, research institutions and funders to accept, store, curate and disseminate this metadata, and Crossref issued what is known as a persistent identifier (the DOI is a specific example of such a PID) to identify the metadata records.