About PhySH

PhySH (Physics Subject Headings) is a physics classification scheme developed by the American Physical Society (APS) to organize journal, meeting, and other content by topic. PhySH is a fully open detailed classification scheme for physics. It was initially developed to meet the specific goals of the APS for journal, meeting, and other content; it is also available for use by the broader community.

As explained below, PhySH consists of concepts used to label entities such as journal articles. At the top level, concepts are organized along two dimensions: Facets (Research Areas, Physical Systems, etc.) and Disciplines. In addition, the concepts are linked to each other in a flexible hierarchy reflecting the broader/narrower relationships among them. Relationships can also span across the hierarchies to identify related concepts.

The infographic on the PhySH homepage shows the general relationship among concepts, disciplines, and facets. Browse PhySH to see how it is organized in detail; a search capability is also incorporated in the browse page.

PhySH will continue to evolve over time, and we encourage physicists to help us keep PhySH up to date. Please use the Contribute link at the top of the page.

Authors submitting to APS journals should consult these guidelines.


APS undertook the development of PhySH to achieve the following goals:

  • Cover all of physics PhySH is intended to cover the full breadth of physics.
  • Facilitate finding relevant content Content properly tagged with PhySH is intended to enable new and useful ways to browse and search the content while providing the underpinnings for recommendation systems and other personalized services.
  • Support linked data PhySH is intended to conform with best practices for linked data, a way of providing structured metadata that can be read and acted upon by computers.
  • Be modular and extensible PhySH is intended to be scoped and implemented in a manner that allows seamless integration with other classification schemes. For example, an independent taxonomy for chemical substances or astronomical objects should be relatively easy to append to PhySH.
  • Replace PACS PhySH is a replacement for an older physics classifiation known as PACS. APS used alpha-numeric PACS codes for about 40 years to classify journal content, especially for internal use during the peer-review process. PACS ceased development in 2010 and so did not reflect continuing developments in physics research. In addition, PACS was not a suitable foundation for the other goals listed here.


The above goals have guided the design and implementation of PhySH as a faceted classification scheme in which concepts grouped into a flexible hierarchy (each concept belong to more than one facet). Furthermore, each concept is assigned to one or more disciplines, which aid in filtering and searching the full scheme.

Central components

  • Concepts are the fundamental building blocks used for classification. Superficially, a concept looks like a simple term or label that is applied to the item being classified, but in fact they are properly thought of as entities with multiple attributes including:
    • Label
    • Alternate labels
    • Unique ID (technically, a URI that is a resolvable URL)
    • Broader and narrower concepts (creating hierarchies of concepts)
    • Related concepts
  • Facets are broad groupings of concepts according to the general role they serve. The current PhySH facets are:
    • Research Areas
    • Physical Systems
    • Properties
    • Techniques (Computational, Experimental, and Theoretical)
    • Professional Topics

Concepts are assigned to one or more facets according to the role(s) they currently most commonly serve. If a particular concept is commonly used as, for example, a technique in one discipline but an active area of research in another, then it may be represented as both a Research Area and a Technique. See for example Solitons.

  • Disciplines are specialties within physics used to narrow the list of concepts. Concepts can belong to more than one discipline.

Other aspects

  • Hierarchy of broader and narrower concepts In PhySH, the concepts are locally organized in hierarchies within the facets. Broader (more general) concepts are linked to narrower (more specific) concepts deeper in the hierarchy.
  • Related concepts Concepts that are related to each other by their physics context but do not appear under the same facet or discipline are linked together within PhySH.
  • Concepts are “simple” Generally, rather than having complex terms that combine multiple aspects into a single label, the organization of concepts into facets allows for more flexible tagging by using a combination of multiple, simple concepts from one or more facets.
  • Concept identifiers are permanent Each concept in PhySH has a unique, permanent identifier which is a registered DOI - for example https://doi.org/10.29172/26ed7afc-8635-4637-a339-8d0a7cb75be1 is the full URI identifier for the concept “Cosmology”.

Development for public release

The main use of PhySH has been to classify manuscripts within the APS peer-review process and in published journal articles. The assigned concepts are used to ensure articles are routed to the most appropriate handling editor who is knowledgeable in that area. They also help editors in finding similar articles previously submitted and in finding suitable referees.

The identified facets and disciplines and roughly 3,000 concepts were added to PhySH through an iterative process over several years. Many APS journal editors were involved in this process, lending their expertise in the various subfields in physics. We have also made adjustments in response to suggestions from authors using PhySH to classify their submissions, and suggestions from other outside contributors. Once the pace of change had slowed sufficiently we felt the time was right for a public release.


The name PhySH is in analogy to MeSH-Medical Subject Headings, the U.S. National Library of Medicine’s controlled vocabulary thesaurus.