PubMed Central (PMC) is a free

digital repository A digital library, also called an online library, an internet library, a digital repository, or a digital collection is an online database of digital objects that can include text, still images, audio, video, digital documents, or other digital m ...

that archives

open access Open access (OA) is a set of principles and a range of practices through which research outputs are distributed online, free of access charges or other barriers. With open access strictly defined (according to the 2001 definition), or libre op ...

full-text scholarly articles that have been published in

biomedical Biomedicine (also referred to as Western medicine, mainstream medicine or conventional medicine)

and

life sciences This list of life sciences comprises the branches of science that involve the scientific study of life – such as microorganisms, plants, and animals including human beings. This science is one of the two major branches of natural science, th ...

journals. As one of the major research databases developed by the

National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. Th ...

(NCBI), PubMed Central is more than a document repository. Submissions to PMC are indexed and formatted for enhanced

metadata Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata – the descriptive ...

, medical

ontology In metaphysics, ontology is the philosophy, philosophical study of being, as well as related concepts such as existence, Becoming (philosophy), becoming, and reality. Ontology addresses questions like how entities are grouped into Category ...

, and unique identifiers which enrich the

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...

structured data for each article. Content within PMC can be linked to other NCBI databases and accessed via Entrez search and retrieval systems, further enhancing the public's ability to discover, read and build upon its biomedical knowledge. PubMed Central is distinct from

PubMed PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine (NLM) at the National Institutes of Health maintai ...

. PubMed Central is a free digital archive of full articles, accessible to anyone from anywhere via a web browser (with varying provisions for reuse). Conversely, although PubMed is a searchable database of biomedical citations and abstracts, the full-text article resides elsewhere (in print or online, free or behind a subscriber

paywall A paywall is a method of restricting access to content, with a purchase or a paid subscription, especially news. Beginning in the mid-2010s, newspapers started implementing paywalls on their websites as a way to increase revenue after years of ...

). , the PMC archive contained over 5.2 million articles, with contributions coming from publishers or authors depositing their manuscripts into the repository per the NIH Public Access Policy. Earlier data shows that from January 2013 to January 2014 author-initiated deposits exceeded 103,000 papers during a 12-month period. PMC identifies about 4,000 journals which participate in some capacity to deposit their published content into the PMC repository. Some publishers delay the release of their articles on PubMed Central for a set time after publication, referred to as an "embargo period", ranging from a few months to a few years depending on the journal. (Embargoes of six to twelve months are the most common.) PubMed Central is a key example of "systematic external distribution by a third party", which is still prohibited by the contributor agreements of many publishers.

Adoption

Launched in February 2000, the repository has grown rapidly as the NIH Public Access Policy is designed to make all research funded by the

National Institutes of Health The National Institutes of Health, commonly referred to as NIH (with each letter pronounced individually), is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the lat ...

(NIH) freely accessible to anyone, and, in addition, many publishers are working cooperatively with the NIH to provide free access to their works. In late 2007, the Consolidated Appropriations Act of 2008 (H.R. 2764) was signed into law and included a provision requiring the NIH to modify its policies and require inclusion into PubMed Central complete electronic copies of their peer-reviewed research and findings from NIH-funded research. These articles are required to be included within 12 months of publication. This is the first time the US government has required an agency to provide

to research and is an evolution from the 2005 policy, in which the NIH asked researchers to voluntarily add their research to PubMed Central. A UK version of the PubMed Central system, UK PubMed Central (UKPMC), has been developed by the

Wellcome Trust The Wellcome Trust is a charitable foundation focused on health research based in London, in the United Kingdom. It was established in 1936 with legacies from the pharmaceutical magnate Henry Wellcome (founder of one of the predecessors of Glaxo ...

and the

British Library The British Library is the national library of the United Kingdom and is one of the largest libraries in the world. It is estimated to contain between 170 and 200 million items from many countries. As a legal deposit library, the Briti ...

as part of a nine-strong group of UK research funders. This system went live in January 2007. On 1 November 2012, it became Europe PubMed Central. The Canadian member of the PubMed Central International network, PubMed Central Canada, was launched in October 2009. The

National Library of Medicine The United States National Library of Medicine (NLM), operated by the United States federal government, is the world's largest medical library. Located in Bethesda, Maryland, the NLM is an institute within the National Institutes of Health. Its ...

"NLM Journal Publishing Tag Set" journal article

markup language Markup language refers to a text-encoding system consisting of a set of symbols inserted in a text document to control its structure, formatting, or the relationship between its parts. Markup is often used to control the display of the document ...

is freely available. The

Association of Learned and Professional Society Publishers The Association of Learned and Professional Society Publishers (ALPSP) is an international trade association of non-profit publishers created in 1972. It is the largest association of scholarly and professional publishers in the world, with nearl ...

comments that "it is likely to become the standard for preparing scholarly content for both books and journals". A related DTD is available for books. The

Library of Congress The Library of Congress (LOC) is the research library that officially serves the United States Congress and is the ''de facto'' national library of the United States. It is the oldest federal cultural institution in the country. The libra ...

and the British Library have announced support for the NLM DTD. It has also been popular with journal service providers. With the release of public access plans for many agencies beyond NIH, PMC is in the process of becoming the repository for a wider variety of articles. This includes NASA content, with the interface branded as "PubSpace".

Technology

Articles are sent to PubMed Central by publishers in

SGML The Standard Generalized Markup Language (SGML; ISO 8879:1986) is a standard for defining generalized markup languages for documents. ISO 8879 Annex A.1 states that generalized markup is "based on two postulates": * Declarative: Markup should ...

, using a variety of article DTDs. Older and larger publishers may have their own established in-house DTDs, but many publishers use the NLM Journal Publishing DTD (see above). Received articles are converted via

XSLT XSLT (Extensible Stylesheet Language Transformations) is a language originally designed for transforming XML documents into other XML documents, or other formats such as HTML for web pages, plain text or XSL Formatting Objects, which may subseq ...

to the very similar NLM Archiving and Interchange DTD. This process may reveal errors that are reported back to the publisher for correction. Graphics are also converted to standard formats and sizes. The original and converted forms are archived. The converted form is moved into a relational database, along with associated files for graphics, multimedia, or other associated data. Many publishers also provide

PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...

of their articles, and these are made available without change. Bibliographic citations are parsed and automatically linked to the relevant abstracts in PubMed, articles in PubMed Central, and resources on publishers' Web sites. PubMed links also lead to PubMed Central. Unresolvable references, such as to journals or particular articles not yet available at one of these sources, are tracked in the database and automatically come "live" when the resources become available. An in-house indexing system provides search capability, and is aware of biological and

medical terminology Medical terminology is a language used to precisely describe the human body including all its components, processes, conditions affecting it, and procedures performed upon it. Medical terminology is used in the field of medicine Medical terminolog ...

, such as generic vs. proprietary drug names, and alternate names for organisms, diseases and anatomical parts. When a user accesses a journal issue, a table of contents is automatically generated by retrieving all articles, letters, editorials, etc. for that issue. When an actual item such as an article is reached, PubMed Central converts the NLM markup to

HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaS ...

for delivery, and provides links to related data objects. This is feasible because the variety of incoming data has first been converted to standard DTDs and graphic formats. In a separate submission stream, NIH-funded authors may deposit articles into PubMed Central using the NIH Manuscript Submission (NIHMS). Articles thus submitted typically go through XML markup in order to be converted to NLM DTD.

Reception

Reactions to PubMed Central among the scholarly publishing community range between a genuine enthusiasm by some, to cautious concern by others. While PMC is a welcome partner to open access publishers in its ability to augment the discovery and dissemination of biomedical knowledge, that same truth causes others to worry about traffic being diverted from the published version of record, the economic consequences of less readership, as well as the effect on maintaining a community of scholars within learned societies. A 2013 analysis found strong evidence that public repositories of published articles were responsible for "drawing significant numbers of readers away from journal websites" and that "the effect of PMC is growing over time". Libraries, universities, open access supporters, consumer health advocacy groups, and patient rights organizations have applauded PubMed Central, and hope to see similar public access repositories developed by other federal funding agencies so to freely share any research publications that were the result of taxpayer support. The Antelman study of open access publishing found that in philosophy, political science, electrical and electronic engineering and mathematics,

papers had a greater research impact. A randomised trial found an increase in content downloads of open access papers, with no citation advantage over subscription access one year after publication. The NIH policy and open access repository work has inspired a 2013 presidential directive which has sparked action in other federal agencies as well. In March 2020, PubMed Central accelerated its deposit procedures for the full text of publications on

coronavirus Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the co ...

. The NLM did so upon request from the White House

Office of Science and Technology Policy An office is a space where an organization's employees perform administrative work in order to support and realize objects and goals of the organization. The word "office" may also denote a position within an organization with specific d ...

and international scientists to improve access for scientists, healthcare providers, data mining innovators, AI healthcare researchers, and the general public.

PMCID

The PMCID (PubMed Central identifier), also known as the PMC reference number, is a

bibliographic Bibliography (from and ), as a discipline, is traditionally the academic study of books as physical, cultural objects; in this sense, it is also known as bibliology (from ). English author and bibliographer John Carter describes ''bibliography ...

identifier An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, where the "object" or class may be an idea, physical countable object (or class thereof), or physical noncountable ...

for the PubMed Central open access database, much like the PMID is the bibliographic identifier for the

database. The two identifiers are distinct however. It consists of "PMC" followed by a string of seven numbers. The format is: * PMCID: PMC1852221 Authors applying for NIH awards must include the PMCID in their application.

References

External links