Digital System of Units
D-SI
FAIR data formats, services, and tools building an anchor of trust for processing international units of measurement in digital applications for science and technology.
Status: Foundational technology, steadily growing tool stack
D-SI Metadata Model and implementations
PTB’s D-SI metadata model provides universal, easy-to-use, unambiguous, and save building blocks for the digital representation and exchange of metrological data. Machine- and human-useable reference implementations of these building blocks are provided for formats XML SCHEME, JSON LINKED DATA and Semantic-Web compatible Ontologies.
D-SI Metadata Model
Common conceptual models for metrological data and associated metadata based on recommendations from the International System of Units and metrological guidelines.
Version: 2 (long term stable)
D-SI XML Scheme
XML Implementation of D-SI
Version: 2.2.1(long term stable)
SIS Ontology
OWL Ontology implementation of D-SI in RDF (TURTLE)
Version: v0.2.1(beta)
D-SI LD
JSON-LD implementation of the D-SI, linking XSD and Ontology (provided as JSON-LD context file)
Version: 2.2.1 (beta, linked to XML Schema version)
Interoperability Framework
In response to Resolution B of the 27th CGPM on the global Digital Transformation of the International System of Units, the D-SI is fostering interoperability of measurement data across digital developments of an international scientific and quality infrastructure. Data, services, and tools are enabled to access an internationally established Interoperability Framework.
D-SI Converter (DME)
Software libraries, command-line-service and web-service for conversion between units and unit representation systems. This service is a Digital Metrological Expert tool. It supports automated conversion and provides metrologically traceable reports for results of conversions.
(Project start in February 2026)
Legacy work such as the SI Reference Point to D-SI transfromer and the D-SI unit tool are being harmonized with this work.
D-SI Constants
Web service providing values of physical and mathematical constants in the D-SI XML format. This service concludes legacy work from project SmartCom D-SI-based list of constants
BIPM SI Reference Point
Official international digital reference for the definition of the SI. Developped and operated by the BIPM. Used as reference for D-SI units.
Version 1.0.5 beta
IEC-CDD Units of Measurement Dictionary
Registry of units of measurement used as D-SI reference for conversion data.
Version 2.0018.0002
QUDT Ontology
Registry of units of measurement and kinds of quantities. D-SI references of units and kinds of quantities in ontologies.
Version 3.2.1