Some of you who have submitted content to us during the first two months of 2021 may have experienced content registration delays. We noticed; you did, too.
The time between us receiving XML from members, to the content being registered with us and the DOI resolving to the correct resolution URL, is usually a matter of minutes. Some submissions take longer - for example, book registrations with large reference lists, or very large files from larger publishers can take up to 24 to 48 hours to process.
TL;DR: We have a Community Forum (yay!), you can come and join it here: community.crossref.org.
Community is fundamental to us at Crossref, we wouldn’t be where we are or achieve the great things we do without the involvement of you, our diverse and engaged members and users. Crossref was founded as a collaboration of publishers with the shared goal of making links between research outputs easier, building a foundational infrastructure making research easier to find, cite, link, assess, and re-use.
Event Data uncovers links between Crossref-registered DOIs and diverse places where they are mentioned across the internet. Whereas a citation links one research article to another, events are a way to create links to locations such as news articles, data sets, Wikipedia entries, and social media mentions. We’ve collected events for several years and make them openly available via an API for anyone to access, as well as creating open logs of how we found each event.
2020 wasn’t all bad. In April of last year, we released our first public data file. Though Crossref metadata is always openly available––and our board recently cemented this by voting to adopt the Principles of Open Scholarly Infrastructure (POSI)––we’ve decided to release an updated file. This will provide a more efficient way to get such a large volume of records. The file (JSON records, 102.6GB) is now available, with thanks once again to Academic Torrents.
These connections may consist of citations, or refer to publications which do not always exist as a single content item (its parts may be produced, curated, and published by different organizations and separate activities). Making these connections creates linked data, which is useful because it establishes associations and context.
Crossref has also introduced other interlinking services that address specific types of relationships:
Components allow for the assignment of DOIs to the component parts of a publication (figures, tables, images) which may lead to their reuse.
Crossmark supports the connection of updates which have a material effect on the original work, for example: updates, corrections, and retractions.
Funding data supports identifying the organization that financially supports the research behind a specific publication.
Peer reviews support the host of outputs made publicly available about published scholarly content, for example: referee reports, decision letters, and author responses.
These and other Crossref services create relationships between content items; however, they share two characteristics that restrict their ability to define relationships:
Both items involved in a relationship must be identified by Crossref-assigned DOIs.
The types of relationships are dictated by the mission of the specific Crossref service.
The following modifications and new services developed in response to these two limitations:
Allow non-Crossref DOIs to be deposited in an item’s (article/chapter/paper) list of citations.
Support the creation of general typed relationships between items with a Crossref DOI, and other content items with a variety of identifiers.
We maintain an expansive set of relationship types to support the various content items that a research object, like a journal article, might link to. For data and software, we ask you to provide the following information:
identifier of the dataset/software
identifier type: DOI, Accession, PURL, ARK, URI, Other (additional identifier types are also accepted beyond those used for data or software, including ARXIV, ECLI, Handle, ISSN, ISBN, PMID, PMCID, and UUID)
relationship type: isSupplementedBy or references (use the former if it was generated as part of the research results)
description of dataset or software
Both Crossref and DataCite use this kind of linking. Data repositories which register their content with DataCite follow the same process and apply the same metadata tags. This means that we achieve direct data interoperability with links in the reverse direction (data and software repositories to journal articles).
The possible relationship types between content items can be as varied as the items themselves. We use a controlled vocabulary to define these relationships, in order to construct an orderly mapped network of content.
This is achieved by (i) an implicit approach where the relation type is a function of a specific service and is declared in the structure of the deposited XML, and (ii) in an explicit approach where the relation type is selected as a value within the deposited metadata.
Reference linking and Cited-by: implicitly creates cites and isCitedBy relationships between a content item and the items in its bibliography
Crossmark: explicit creation of update relations between an item and other items that materially affect it (for example, a retraction)
Funding data: implicit creation of isFundedBy and hasAward relationships between an item and the funding source that supported the underlying research
Linked clinical trials: implicit creation of a belongsTo relationship between and item and a registered clinical trial
Components: implicit creation of a isChildOf relationship between an item and its elemental parts that are assigned their own DOI (limited parent relation typing)
General typed relations: explicitly typed relation between an item with a Crossref DOI and an item with one of several possible identifiers.
Relationship types for associated research objects: intra-work (within a work)
Reciprocal relationship types
Relationship types for associated research objects: inter-work (between works)
Reciprocal relationship types
Related material, such as a protocol
Supplement, such as a dataset generated as part of research results
General typed relations
This service allows for the creation of a typed relationship between an item with a Crossref DOI and another content item. The other item may be represented by another Crossref DOI, a DOI from some other Registration Agency, or an item not identified with a DOI. When DOIs are used, the deposit process will fail if the DOI does not exist. Non-DOI identifiers are not verified.
When DOIs are used, a bidirectional relation is automatically created by Crossref when a relation is created in the deposit of one item in a pair. The DOI with metadata creating the relation is said to be the claimant, the other item does not need to have its metadata directly contain the relationship.
Example: translated article
A single journal article is published in two languages with each being assigned its own DOI. In this example, both are published in the same journal. The original language instance has metadata that contains no indication of the translation instance. The alternative language instance includes in its metadata a relation to the original language instance. Here is a screenshot of the relevant section in the code. Please refer to the code snippet below to see it in context.
<title>Um artigo na língua original, que passa a ser o inglês</title>
<original_language_title language="en">An article in its original language which happens to be English</original_language_title>
<person_name sequence="first" contributor_role="author">
<description>Portuguese translation of an article</description>
<intra_work_relation relationship-type="isTranslationOf" identifier-type="doi">10.5555/original_language</intra_work_relation>
Example: book review
This example has a book review published as an article in the journal The Holocene. The article’s title, taken from the publisher’s site is “Book Review: Understanding the Earth system: compartments, processes and interactions” where this book has the DOI https://0-doi-org.libus.csd.mu.edu/10.1007/978-3-642-56843-5.
A: The current metadata for the review article gives no indication of the actual book being reviewed: