PhySH: Physics Subject Headings Scheme Guide

PhySH, short for Physics Subject Headings, is an open-access classification scheme developed by the American Physical Society (APS) to index physics literature, route submitted manuscripts during peer review, and connect related research. Designed as a flexible, faceted vocabulary rather than a rigid alphanumeric tree, PhySH provides standardized topic terms across all major branches of physics research and adjacent fields such as astronomy. It enables physical science authors, editors, and indexing services to tag manuscripts with persistent digital identifiers and semantic concept relationships.

What it is

PhySH is a controlled vocabulary and classification platform built specifically for the physical sciences. Modeled conceptually on the National Library of Medicine’s Medical Subject Headings (MeSH), PhySH organizes research concepts into an extensible network. Unlike older coding schemes that assigned fixed alphanumeric strings to narrow subject niches, PhySH treats every entry as an independent semantic concept. Each concept possesses a human-readable preferred label, alternate synonymous terms, and a permanent, resolvable URI registered as a digital object identifier with Crossref DOIs under the prefix 10.29172.

In modern scholarly publishing, authors encounter PhySH primarily during manuscript submission to APS journals such as Physical Review Letters and Physical Review A–E, often working alongside manuscript preparation tools like REVTeX. By selecting descriptive concepts from the taxonomy, authors assist journal editorial offices in directing papers to appropriate handling editors and identifying qualified peer reviewers.

Who runs it and what it covers

PhySH is created, developed, and maintained by the American Physical Society (APS). The taxonomy is released openly under the Creative Commons CC0 1.0 Public Domain Dedication, allowing publishers, bibliometric repositories, and institutional libraries to freely adopt, modify, and redistribute the vocabulary without copyright restrictions. The name “PhySH” and its associated logos remain protected trademarks of the APS.

The scope of PhySH encompasses roughly 3,000 distinct concepts organized across two primary organizational axes:

Facets: Five broad groupings that characterize the functional role of a concept:
- Research Areas: Substantive fields of inquiry (for example, Cosmology, Superconductivity, or Quantum Optics).
- Physical Systems: Concrete entities, materials, or environments under study (such as Carbon Nanotubes, Topological Insulators, or Neutron Stars).
- Properties: Specific characteristics or measurable phenomena (including Band Structure, Entanglement, or Superfluidity).
- Techniques: Methodological approaches, divided into Computational, Experimental, and Theoretical techniques (such as Density Functional Theory, X-ray Diffraction, or Renormalization Group).
- Professional Topics: Societal, pedagogical, and organizational aspects of physics practice, such as Physics Education, Ethics, and History of Physics.
Disciplines: Broad subfields of physical science (including Astrophysics, Condensed Matter, Particles & Fields, Plasma Physics, Gravitation, and Quantum Information) that act as filtering lenses over the concept graph. Concepts can span multiple disciplines and facets simultaneously.

How to search or use it

Researchers, authors, and data specialists interact with PhySH through the interactive web portal at physh.org, within journal submission management systems, and via programmatic REST endpoints. To search, explore, and apply PhySH concepts, follow these procedural steps:

Access the Browse Interface: Navigate to the public portal and select the Browse view (physh.org/browse). The landing interface presents physics disciplines alongside facet filters.
Filter by Discipline: Choose your target subfield (such as “Atomic, Molecular & Optical” or “Particles & Fields”) from the discipline menu to restrict visible concepts to relevant areas of inquiry.
Select a Facet Category: Narrow your selection by clicking one of the five facet tabs—Research Areas, Physical Systems, Properties, Techniques, or Professional Topics—to display the hierarchical concept tree.
Locate and Inspect Concepts: Drill down through broader and narrower concept relationships. Clicking any concept label opens its concept profile, displaying alternate labels, narrower sub-topics, related cross-facet concepts, and its permanent DOI.
Apply Concepts During Journal Submission: When uploading a manuscript through APS editorial systems, enter the selected concept names into the submission keyword interface. Authors typically select two to four specific concepts covering the research area, physical system, and primary experimental or theoretical technique. In large experimental papers such as those from mega-collaboration author consortia, standardizing subject headings ensures accurate routing across complex multidisciplinary editorial boards.
Query the Programmatic REST API: Developers and repository managers can retrieve machine-readable JSON representations by sending standard HTTP requests with an Accept: application/json header:
```
curl -H 'Accept: application/json' https://physh.org/concepts/26ed7afc-8635-4637-a339-8d0a7cb75be1
```
To retrieve a concept along with all related concepts, facets, and discipline memberships, append query parameters:
```
curl -H 'Accept: application/json' 'https://physh.org/concepts/26ed7afc-8635-4637-a339-8d0a7cb75be1?include=related,facets,disciplines'
```
Bulk taxonomy dumps are also available via GitHub in JSON-LD (physh.json), RDF Turtle (physh.ttl), and N-Triples (physh.nt) under versioned releases following Semantic Versioning.

Strengths and limits

Evaluating PhySH within research-practice workflows highlights several operational advantages and structural constraints:

Strengths:
- Faceted Flexibility: By decoupling physical systems from experimental techniques and theoretical properties, PhySH avoids the combinatorial explosion inherent in older hierarchical trees. Authors can combine simple concepts rather than searching for pre-composed compound phrases.
- Persistent Identifiers: Assigning registered DOIs to every concept ensures stable persistent linking across publishing platforms, ontologies, and semantic web graphs.
- Open Licensing: The CC0 dedication eliminates licensing barriers, encouraging broad adoption across institutional repositories, preprint servers, and discovery engines.
- Dynamic Versioning: APS maintains a quarterly release cadence using Semantic Versioning (current release version 2.8.0), providing formal deprecation mappings in deprecated.csv when terms evolve.
Limits:
- Domain Scope: PhySH is tailored specifically to physics and astrophysics; it does not provide granular indexing for organic chemistry, cell biology, or clinical medicine.
- Selective Publisher Adoption: While fully integrated across the American Physical Society publishing portfolio, many other major physical science publishers continue to utilize proprietary internal keyword lists or publisher-specific taxonomy schemes.
- Vocabulary Size: With approximately 3,000 concepts, PhySH is more focused than massive multidisciplinary vocabularies like MeSH (over 30,000 descriptors), occasionally requiring authors in emerging frontier subfields to rely on broader parent terms.

Alternatives

Scholarly publishing utilizes multiple classification systems depending on publisher policies, historical traditions, and disciplinary focus. The table below compares PhySH with established subject classification schemes:

Classification Scheme	Governing Organization	Primary Discipline	Structure & Identifier Type	License & Openness
PhySH	American Physical Society (APS)	Physics, Astronomy, Biophysics	Faceted concept graph with persistent DOIs (`10.29172`)	Creative Commons CC0 (Public Domain)
PACS (Retired)	American Institute of Physics (AIP)	Physics and Astronomy	Hierarchical alphanumeric codes (e.g., `03.65.-w`)	Retired in 2010; legacy use only
MeSH	National Library of Medicine (NLM)	Biomedicine and Life Sciences	Hierarchical tree with alphanumeric descriptor numbers	Public domain; updated annually
MSC (Mathematics Subject Classification)	American Mathematical Society (AMS) & zbMATH	Mathematics and Theoretical Physics	Five-character alphanumeric codes (e.g., `81T30`)	Free for scholarly use; periodic revisions (MSC2020)
ACM CCS	Association for Computing Machinery (ACM)	Computer Science and Information Systems	Polyhierarchical ontology with unique concept IDs	Openly available; updated periodically

FAQ

Why did APS replace PACS with PhySH?

The Physics and Astronomy Classification Scheme (PACS) relied on rigid, five-tier alphanumeric codes that became increasingly difficult to maintain as physics subfields converged and interdisciplinary research expanded. PACS was officially discontinued by AIP in 2010. APS developed PhySH to introduce a dynamic, keyword-based faceted network that reflects modern research without legacy alphanumeric constraints.

Is PhySH free to use in institutional repositories?

Yes. APS released PhySH under the Creative Commons CC0 1.0 Universal public domain dedication. Anyone may freely download, index, modify, or embed PhySH concepts into repositories, library catalogs, or discovery software without licensing fees or permissions.

How often is PhySH updated?

PhySH updates follow Semantic Versioning (X.Y.Z). New terms and minor backwards-compatible structural updates occur on a scheduled cadence up to four times per year. Deprecated concepts are recorded in a publicly accessible mapping file (deprecated.csv) that links obsolete terms to their recommended replacements.

Can authors suggest new terms for PhySH?

Yes. Authors and researchers can submit term feedback and proposed additions through the official feedback form linked on physh.org. Proposed concepts are evaluated by APS journal editors and subject matter specialists prior to inclusion in scheduled quarterly releases.

Sources

American Physical Society: About PhySH (Physics Subject Headings), https://physh.org/about (read 2026-11-07).
American Physical Society: PhySH Licensing and Public Domain Notice, https://physh.org/licensing (read 2026-11-07).
American Physical Society: PhySH REST API Documentation and Curl Examples, https://physh.org/apis (read 2026-11-07).
American Physical Society: PhySH Releases, Versioning and Bulk Formats (Version 2.8.0), https://physh.org/releases (read 2026-11-07).