How to use Voc4Cat?¶

Voc4Cat provides persistent identifiers and definitions for catalysis concepts in the machine-readable SKOS format. This page gives an overview of the various ways to access and work with Voc4Cat in your tools, code, and data workflows.

Browsing Voc4Cat online¶

There are several web-based entry points for exploring the vocabulary:

pyLODE HTML documentation – The auto-generated documentation shows the full concept hierarchy, definitions, and relationships. The latest release is the recommended stable reference. A development version is also available and reflects the most current state of the vocabulary.
Skosmos at ZB MED – The Skosmos instance at ZB MED provides search, hierarchical browsing, and a REST API tailored for SKOS vocabularies. It shows the latest published release.
TIB Terminology Service – The TIB service offers an alternative OLS-based interface and API. It also shows the latest published release.

Tip

For SKOS vocabularies, the Skosmos service is recommended because it understands SKOS-specific features such as concept hierarchies, collections, and semantic relations.

Downloading Voc4Cat¶

The vocabulary is available for download in multiple formats. The direct links below are convenient but not permanent – for stable references, use the permanent URLs listed on the main page.

Format	Development version	Latest release
Turtle (.ttl)	dev/voc4cat.ttl	latest/voc4cat.ttl
RDF/XML (.xml)	dev/voc4cat.xml	latest/voc4cat.xml
Excel (.xlsx)	dev/voc4cat.xlsx	–

Content negotiation¶

Content negotiation allows you to request a specific format from the same permanent URL. By setting the Accept header, you can download Turtle, RDF/XML, or get the HTML documentation – all from https://w3id.org/nfdi4cat/voc4cat.

curl

# Download Turtle format
curl -L -H "Accept: text/turtle" -o voc4cat.ttl https://w3id.org/nfdi4cat/voc4cat

# Download RDF/XML format
curl -L -H "Accept: application/rdf+xml" -o voc4cat.xml https://w3id.org/nfdi4cat/voc4cat

# Download a specific release
curl -L -H "Accept: text/turtle" -o voc4cat.ttl https://w3id.org/nfdi4cat/voc4cat/v2025-10-14

Python

import requests

url = "https://w3id.org/nfdi4cat/voc4cat"
r = requests.get(url, headers={"Accept": "text/turtle"})
with open("voc4cat.ttl", "w", encoding="utf-8") as f:
    f.write(r.text)

Note

The development version is rebuilt on every merge to the main branch and reflects the latest accepted changes. Releases are tagged snapshots deposited on Zenodo and published to terminology services. For reproducible references in publications, always use a specific release version.

Using Voc4Cat via terminology service APIs¶

Both Skosmos and TIB provide REST APIs for programmatic access to the vocabulary. The Skosmos REST API is recommended for SKOS vocabularies.

Skosmos REST API examples¶

# Search for concepts by text
curl "https://semanticlookup.zbmed.de/skosmos/rest/v1/voc4cat/search?query=catalysis"

# Get data for a specific concept by IRI
curl "https://semanticlookup.zbmed.de/skosmos/rest/v1/voc4cat/data?uri=https://w3id.org/nfdi4cat/voc4cat_0000001"

# Get narrower concepts of a given concept
curl "https://semanticlookup.zbmed.de/skosmos/rest/v1/voc4cat/narrower?uri=https://w3id.org/nfdi4cat/voc4cat_0000196"

The full Skosmos REST API documentation is available at https://semanticlookup.zbmed.de/skosmos/rest/v1/.

The TIB Terminology Service also offers a REST API; see https://terminology.tib.eu/ts/ontologies/voc4cat for details.

Tip

The NFDI4Cat data repository repo4cat uses the Skosmos REST API to integrate Voc4Cat concepts into its metadata forms.

Working with Voc4Cat in Python¶

The vocabulary can be loaded and queried directly in Python using rdflib:

from rdflib import Graph, Namespace
from rdflib.namespace import SKOS, RDF

g = Graph()
g.parse("https://nfdi4cat.github.io/voc4cat/dev/voc4cat.ttl", format="turtle")

VOC4CAT = Namespace("https://w3id.org/nfdi4cat/voc4cat_")

# List all concepts with their labels
for concept in g.subjects(predicate=RDF.type, object=SKOS.Concept):
    label = g.value(concept, SKOS.prefLabel)
    print(f"{concept} -- {label}")

Tip

For a complete walkthrough – including searching, navigating the hierarchy, SPARQL queries, and visualizing the concept graph – see our Jupyter notebook demo.

To run the notebook locally, install the dependencies from demo/requirements.txt.

Using Voc4Cat in data management tools¶

Voc4Cat concepts can be used to annotate research data in various data management platforms.

repo4cat (Dataverse) – The repo4cat data repository, operated by NFDI4Cat, integrates Voc4Cat via the Skosmos REST API. Researchers can select Voc4Cat concepts when annotating datasets, ensuring consistent and machine-readable metadata.

NOMAD (FAIRMAT) – The nomad-catalysis-plugin integrates Voc4Cat concepts into NOMAD, providing a data schema for heterogeneous catalysis that uses Voc4Cat identifiers for standardized annotation. See the accompanying preprint for details.

LabImotion / Chemotion (NFDI4Chem) – Chemotion is an electronic lab notebook developed within NFDI4Chem that supports vocabulary-based annotation. Using Voc4Cat concepts in Chemotion is a potential future integration.

Note

The list of tools with Voc4Cat integration is growing. If you are using Voc4Cat in a tool not listed here, please let us know by creating an issue.

Using Voc4Cat concepts in data models and ontologies¶

LinkML data models¶

SKOS concepts from Voc4Cat can be referenced as permissible values in LinkML data model schemas. For example, a dataset schema could restrict a field to only accept Voc4Cat concept IRIs:

enums:
  CatalysisResearchField:
    permissible_values:
      photocatalysis:
        meaning: voc4cat:0000001
      electrocatalysis:
        meaning: voc4cat:0000204
      biocatalysis:
        meaning: voc4cat:0000207

See the LinkML documentation for details on using enumerations with external concept identifiers.

A real-world example is the pid4cat-model, which uses Voc4Cat concepts to provide URIs and definitions for its RelationType enumeration.

SKOS concepts in OWL ontologies¶

SKOS concepts are not OWL classes – they represent terms in a vocabulary rather than formal categories in a logical framework. However, SKOS and OWL can be used together. To connect Voc4Cat concepts with classes in an OWL ontology, use SKOS mapping properties such as skos:exactMatch or skos:closeMatch:

ex:PhotocatalysisProcess a owl:Class ;
    skos:exactMatch voc4cat:0000001 .

This approach preserves the distinct roles of the vocabulary (informal, consensus-based definitions) and the ontology (formal logic and reasoning) while making the relationship explicit. See the SKOS Reference for more on mapping properties.

What other topics would you like to read about here? Let us know by creating an issue!