Schemas
UnitsML provides two complementary sets of schema definitions for encoding and validating scientific units of measure.
UnitsML XML Schemas
Authoritative XML schemas (XSD) for encoding scientific units of measure in XML documents. UnitsML XML Schemas validate XML documents that use UnitsML markup, covering SI base units, derived units, and non-SI units.
The schema is designed to be used in combination with other specific schemas through XML namespaces — not as a standalone schema. Developers of other markup languages incorporate UnitsML to address the needs of specific communities such as mathematics, chemistry, and materials science.
Supported unit types
SI Base & Special Derived
meter, second, joule, volt, kilogram, ampere, kelvin, mole, candela
SI Derived Units
square meter, meter per second, newton, pascal, watt, hertz, and more
Non-SI Units
minute, angstrom, inch, pound, calorie, atmosphere, and others
Schema versions
| Version | Status | Description |
|---|---|---|
| UnitsML 1.0 | Current | Latest stable release |
| UnitsML 1.0-CSD04 | Draft | Committee Specification Draft 04 |
| UnitsML 0.9.x | Historical | Earlier development versions |
| UnitsML-Lite | Deprecated | Simplified subset |
UnitsDB YAML Schemas
YAML schemas that define the structure and validation rules for UnitsDB — the authoritative database of scientific units. Each schema validates one of the six entity types:
| Schema | Entity | Defines |
|---|---|---|
units-schema.yaml | Unit | Measurement units with identifiers, symbols, scale/system references, dimensional composition |
quantities-schema.yaml | Quantity | Measurable properties (length, mass, force) with dimension references |
dimensions-schema.yaml | Dimension | SI base quantity dimensional powers (L, M, T, I, Θ, N, J) |
prefixes-schema.yaml | Prefix | SI decimal (kilo, milli) and binary (kibi, mebi) scaling factors |
scales-schema.yaml | Scale | Measurement scale properties (continuous, ordered, logarithmic, interval, ratio) |
unit_systems-schema.yaml | Unit System | Systems of measurement (SI, CGS) with base unit definitions |
Shared patterns
All entity schemas share common structures:
identifiers[]— Cross-system IDs withtypeenum (nist, unitsml, ucum, si-digital-framework)names[]— Multilingual names with ISO language codesreferences[]— Informative and normative external references
Unit, Prefix, and Dimension schemas include 6-format symbol representations: latex, unicode, ascii, html, id, mathml.
Related resources
- UnitsDB — browse the complete database with 716 entities
- How UnitsML Works — technical architecture overview
- UnitsML Guide — usage guide with examples
- unitsml-ruby — Ruby gem for programmatic access