For existing users, or those intending to use QUDT - YOUR OPINION NEEDED!

First question

We are trying to get a better feel for how people are using, or intending to use QUDT. Do you...

1. Use QUDT with the OWL schema
2. Use QUDT with the SHACL schema
3. Use just the QUDT vocabularies as persistent unique identifiers for units, etc.
4. Use QUDT in some other way

Please answer our brief poll here

Second question

For the OWL users, we are considering simplifying the OWL schema for several reasons.

1. We perform all of our development and maintenance work using the SHACL schemas
2. We have been told that few users are actually trying to do OWL reasoning on QUDT
3. The OWL axioms concerning object properties is a maintenance time sink

Before we take any action, we need to hear from you! We are considering one of the following options:

1. Remove all axioms from the OWL schema, that is restriction classes for allValuesFrom, someValuesFrom and cardinality constraints, and perhaps a small number of other axioms. Instead adopt a version of RDFS-plus which would necessitate expressing domain(s) and range(s) on properties.
2. Leave things as they are, recognizing that errors occasionally creep in (e.g. try loading it in Protege right now - there are 3 errors)

The vocabularies are all just RDFS, so they remain untouched by this change.

Please give us feedback by entering a comment on our GitHub Discussions page here. We will wait for your feedback until December 15, 2025 before deciding on our course of action.

...now back to our normal README:

QUDT - Quantities, Units, Dimensions and DataTypes

Quick-Start Guide

There are three ways to bring the QUDT ontology into your environment.

1. Download the latest GitHub Release here and load one of:

• QUDT-all-in-one-SHACL.ttl

• QUDT-all-in-one-OWL.ttl

  depending on whether you are using OWL or SHACL as your modeling approach.

2. Use the resolved graph and instance URIs, one of:
   • http://qudt.org/shacl/qudt-all
   • http://qudt.org/qudt-all
3. Use GitHub fork to get the sources and build them using the instructions here.

Overview

This QUDT¹ public repository contains the schema and vocabulary source files for the graphs making up the QUDT collection. It is probably the most convenient way for software developers to include the QUDT ontologies in their work, and is the most up-to-date. However, for those who prefer the linked data world, each QUDT graph is also available in both a versioned and an unversioned form on the qudt.org website.

DOI reference for citations: https://doi.org/10.25504/FAIRsharing.d3pqw7

Here is the core design pattern of the QUDT ontology:

Our current plan is to deliver this material in even more powerful ways. The website now hosts a SPARQL endpoint, as well as an engine supporting SPARQL and GraphQL queries. Fully resolvable URIs at the graph and instance level are available online. Eventually we will also support resolvable class URIs as well. We are also creating a series of User Guides on the wiki for this repository.

We encourage you to get involved. If you have particular needs or see errors, please create an Issue and/or make changes or additions yourself (please see our Wiki for more detailed instructions, and specifically the Units Submission Guide if you would like to suggest additional units.) We are a volunteer-staffed effort, but we do have infrastructural expenses. Please consider making a DONATION.

Installation instructions

Installing QUDT for Consumers

Installing QUDT for Contributors

SHACL Validation for QUDT Users versus QUDT Developers

QUDT SHACL for users is supported by a set of validation rules that check for references to deprecated instances or properties and recommend the updated instance or property.

QUDT SHACL for contributors (accessed by using the individual graphs rather than QUDT-all-in-one-SHACL.ttl in the Release or fork) is supported by a much larger set of validation rules that check the integrity of the QUDT ontologies themselves.

Protege Users

The QUDT ontologies have been tested to load without error in Protege 5.6.4.

To load QUDT into Protege, choose "Open from URI" from the file menu, and enter http://qudt.org/qudt-all

This will load the latest version of the distribution file containing the OWL schema and all vocabularies for QUDT. You can also load a specific version by including the semantic version number, such as http://qudt.org/3.1.4/qudt-all

Ontology libraries

Please note that various libraries exhibit different behaviors when importing the QUDT ontology, see this discussion.

Status

Please see the documentation supporting each Release. There are also New Features and Releases discussed in the Discussions section.

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¹ QUDT.org is a 501(c)(3) not-for-profit organization founded to provide semantic specifications for units of measure, quantity kind, dimensions and data types. QUDT is an advocate for the development and implementation of standards to quantify data expressed in RDF and JSON. Our mission is to improve interoperability of data and the specification of information structures through industry standards for Units of Measure, Quantity Kinds, Dimensions and Data Types. Sponsorships are greatly appreciated!

QUDT.org is a member of the World Wide Web Consortium (W3C)

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Last updated by: Steve Ray ([email protected])

Last updated: July 30, 2025