About PhySH

PhySH (Physics Subject Headings) is a physics classification scheme developed by the American Physical Society to organize journal, meeting, and other content by topic. The development of PhySH is motivated by the lack of a fully open, high quality classification scheme for physics. It is intended initially to meet the specific goals of the APS for our journal, meeting, and other content. A longer term goal is to make it 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 is currently under development, and in this initial phase we encourage the community to help us improve PhySH by providing feedback on the content, structure, and user friendliness of PhySH. Please use the Feedback 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.

  • Replace PACS PhySH is intended to function as a full replacement for PACS. APS has long used numeric PACS codes to classify journal content, especially for internal use during the peer-review process. As of 2010, PACS is no longer maintained leaving significant gaps (e.g., topological insulators, Weyl and Dirac semimetals, spin caloritronics, etc. are not in PACS). In addition, PACS is not a suitable foundation for the other goals listed here.

  • 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.


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 will be given a unique, permanent identifier. Right now, these are URIs within the physh.aps.org namespace (they are resolvable as URLs). As we move towards a more general release which would allow for exporting PhySH, we expect to switch to DOIs as the primary identifiers.

Current focus

Right now, the main use of PhySH is to classify manuscripts within the APS peer-review process and, ultimately, published journal articles. The assigned concepts will be used for ensuring 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.

As one might expect with something so new, the refinement of PhySH is still very much underway. The facets and disciplines have been identified and almost 3,000 concepts have been added to PhySH through an iterative process that is still ongoing. Many APS journal editors are involved in this process, primarily by lending their expertise in the various subfields in physics. The assignment of concepts to the various facets can be rather subjective. Thus, we expect to make many adjustments to PhySH as we receive feedback from the community (especially authors using PhySH to classify their submissions) and as we incorporate PhySH into the APS journal websites. As we iteratively refine PhySH over the coming months, the rate of new concept additions, concept reassignments within facets, and new relationships among concepts should abate significantly.


Beyond the ongoing refinement of PhySH, APS will be working to integrate PhySH into our journal platform by building new features based upon the classification of articles. We hope to improve finding relevant content across our journals, which often have overlapping scopes.

As we have been developing PhySH, we have been careful to implement it in a manner consistent with the eventual public release of PhySH for general use by others. The timing of any such release is unclear at this point as it is our intention to go through several iterations of refinement first.


PhySH is copyrighted with all rights reserved by the American Physical Society. We are still considering what license we would use for any public release of PhySH.


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