CASRAI Dictionary

Tag: scholarly metadata

  • Crossref: the metadata backbone of scholarly communication

    When you click a DOI link and arrive reliably at an article years after it was published, when a reference list resolves into live links, when a funder can see which papers acknowledged its support, or when a reader is warned that a paper has been corrected or retracted, a single piece of infrastructure is usually working quietly in the background. That infrastructure is Crossref: the not-for-profit DOI registration agency through which a large share of the world’s scholarly literature is registered and described. Crossref is rarely visible to researchers, yet it underpins a great deal of how scholarship is found, cited and connected. This article explains what Crossref does and why it matters, drawing on the research information systems domain of the CASRAI Dictionary.

    What Crossref actually is

    Crossref is a membership organisation, founded by publishers, that operates as a registration agency for Digital Object Identifiers (DOIs). When a publisher registers an article, book chapter, conference paper or other scholarly work with Crossref, two things happen: the work receives a persistent DOI that will resolve to its current location indefinitely, and the publisher deposits structured metadata describing the work — its title, authors, publication venue, dates, references, and increasingly its funding, licences and identifiers for the people and organisations involved. The DOI is the visible part; the metadata is the substance. Crossref’s real product is not the identifier alone but the enormous, openly queryable corpus of interlinked metadata that the identifiers make navigable.

    DOIs and persistent linking

    The foundational service is persistent identification. A DOI is a stable handle that points to a work regardless of where the publisher later moves the content; update the target once in the registry and every citation of that DOI continues to resolve. This solves the link-rot problem that plagues ordinary web addresses, where URLs decay as sites are reorganised. Because the DOI is persistent and resolvable, it can serve as a reliable anchor for everything else: a reference can cite it, a dataset record can link to it, an author’s ORCID profile can list it, and all of those references remain valid over time. Persistent identification is the precondition for every other connection Crossref enables.

    The metadata services that build on DOIs

    On top of the DOI, Crossref runs a family of services that turn isolated records into a connected graph:

    • Reference linking and Cited-by. When publishers deposit the reference lists of their articles, Crossref matches those references to registered DOIs. This makes reference lists resolvable, and it powers Cited-by, which lets a work surface the later works that cite it — citation relationships derived directly from deposited metadata.
    • The Open Funder Registry. A controlled list of funding bodies that lets publishers record, in a standardised form, who funded the research behind a paper. Standardised funder names are what make it possible to ask reliably which outputs a given funder supported, rather than guessing from inconsistent free-text acknowledgements.
    • Crossmark. A service that gives readers a way to check whether they are looking at the current version of a work and to see its update status — corrections, retractions, expressions of concern. Crossmark surfaces the scholarly record’s changes rather than letting a superseded version circulate unflagged.
    • Grant linking. Funders can register their grants with Crossref and receive DOIs for them, and output metadata can reference those grants — connecting published works back to the awards that supported them in a machine-readable way.

    Why open metadata matters

    What gives Crossref its outsized importance is that its metadata is openly available through a public interface that anyone can query. This openness means the metadata is not locked inside one company’s product but is a shared resource that discovery services, repositories, research-information systems, analytics tools and researchers themselves can all build upon. A reference manager that resolves citations, an institutional system that ingests a researcher’s publications, a discovery layer that links related works — all of these draw on the same open Crossref corpus. The value compounds: each well-formed deposit enriches a commons that the whole community uses, which is why the quality of the metadata publishers deposit matters as much as the existence of the DOI.

    Crossref alongside other identifier systems

    Crossref does not work alone. It interoperates with the other persistent identifiers that describe the research world: ORCID for people, ROR for organisations, and DataCite for datasets and other research outputs. An article’s Crossref record can carry the ORCID iDs of its authors and the ROR identifiers of their institutions, while a DataCite record for a dataset can link to the Crossref-registered article that analyses it. Crossref and DataCite together cover much of the scholarly output graph — broadly, the literature and the data — and their alignment is part of what lets the whole network be traversed. Crossref’s place in this federated arrangement is described in our work on Crossref and federation.

    Crediting the work behind the record

    Rich Crossref metadata can carry more than bibliographic facts; it can carry information about contribution. As publishers increasingly deposit structured contributorship alongside author lists, the CRediT taxonomy — whose full set of contribution types is described in our overview of the CRediT roles — can travel with the article record itself, so that who-did-what becomes part of the persistent, openly queryable metadata rather than prose buried in a paper. For any of this to interoperate, a metadata element must mean the same thing wherever it appears. That consistency is what the CASRAI Dictionary exists to provide: a stable vocabulary so that the funding, contribution and relationship information flowing through Crossref is understood identically across the systems that consume it. Crossref supplies the connective metadata; a shared dictionary keeps it legible.

  • ISBN, ISSN and identifiers for books and journals

    The persistent identifier most familiar to today’s researchers is the DOI, attached to journal articles, datasets and a growing range of outputs. But the idea of giving a publication a stable, standardised identifier is far older, and two of the most successful examples predate the digital scholarly record by decades. The ISBN and the ISSN — the identifiers for books and for serials respectively — are international standards that quietly organise the worlds of publishing, libraries and the book trade, and they remain essential to the scholarly record, particularly for the monographs and journals that the article-centric DOI does not directly address. Understanding what each one identifies, and how they relate to the newer identifiers, is part of being literate in the persistent identifiers domain of the CASRAI Dictionary.

    The ISBN: identifying books

    The International Standard Book Number (ISBN), defined by the international standard ISO 2108, identifies a specific book or book-like product. The key word is specific. An ISBN identifies a particular edition in a particular form: a hardback, a paperback and an e-book of the same title each receive their own distinct ISBN, because they are different products that a bookseller, library or reader needs to distinguish. This granularity reflects the ISBN’s origins in the book trade, where ordering, stocking and selling demand that each product be unambiguously identifiable. For scholarship, the ISBN matters above all for the monograph — the scholarly book that remains a primary form of output in the humanities and many social sciences — giving the book-length output a stable handle comparable to the article’s.

    The ISSN: identifying serials

    The International Standard Serial Number (ISSN), defined by ISO 3297, identifies a serial — a publication issued in a continuing sequence, such as a journal, magazine or other periodical. Here the unit of identification is different and important to grasp. An ISSN identifies the title as a whole, the ongoing publication itself, not any single issue or article within it. The journal has one ISSN that persists across all its issues and volumes; individual articles are identified by other means. The ISSN system also handles the reality that serials appear in different media: a journal published in both print and online forms is typically assigned distinct ISSNs for each, with a linking mechanism connecting them as expressions of the same title. The ISSN lets libraries, indexes, agents and discovery systems refer to a journal unambiguously across decades and across changes of publisher or format.

    How they differ from DOIs

    The crucial conceptual point is that these identifiers operate at different levels of granularity, and they complement rather than compete with one another:

    • An ISSN identifies a journal — the whole continuing publication.
    • An ISBN identifies a book — a specific edition of a specific title.
    • A DOI typically identifies an individual item — a single article, chapter, dataset or other discrete output — and is designed above all to resolve to a current location online.

    Seen this way, the question is not which identifier is “better” but what each is for. The ISSN and ISBN identify the container or the work at the level of the journal title or the book; the DOI identifies the individual item and provides actionable resolution — click a DOI and it takes you to the thing. A complete picture of a scholarly book chapter might involve the ISBN of the book, the ISSN of a series it belongs to, and a DOI for the chapter itself, each doing its own job.

    How they connect

    These systems increasingly work together rather than in isolation. A DOI registered for a journal article carries metadata that includes the journal’s ISSN, tying the item-level identifier to the title-level one. A DOI for a book chapter can reference the book’s ISBN. This linking lets discovery and citation systems assemble a coherent view: knowing that this article (DOI) appeared in that journal (ISSN), or that this chapter (DOI) belongs to that book (ISBN). The identifiers form a layered structure — title-level and item-level — and the value comes from the connections between the layers. For monographs in particular, the maturing of book-level DOIs alongside the long-established ISBN has helped scholarly books participate more fully in the citation and discovery ecosystem articles have long enjoyed.

    Why this matters for the record

    Getting these identifiers right is not pedantry; it is what makes the scholarly record navigable. Accurate ISSNs let a journal’s entire run be tracked and its articles correctly attributed to it; accurate ISBNs let scholarly books and their editions be found, ordered, preserved and cited; and the connection of both to DOIs lets the item and its container be linked. Where these identifiers are missing, wrong or inconsistently recorded, citations break, holdings are confused and outputs become harder to find — problems that fall especially hard on book-based disciplines. The wider persistent-identifier landscape, from ORCID for people to ROR for organisations, is the subject of much of this domain, and the ISBN and ISSN are among its oldest and most reliable members.

    A consistent vocabulary for identifiers

    For these identifiers to do their work across publishers, libraries, indexes and research systems, the metadata around them must be described consistently — which identifier type is which, what it identifies, and how the levels relate. That consistency is what the CASRAI Dictionary provides: a shared vocabulary so that an ISBN, an ISSN and a DOI are each understood for what they are wherever they appear. And because every book and journal rests on the contributions of authors, editors and others, the work behind them can be described in the same shared framework — the CRediT taxonomy. Long before the digital age, the ISBN and ISSN showed the power of giving publications stable, standardised identities; they remain quietly indispensable to a scholarly record that now spans articles, books, journals and far beyond.