UnitsDB

Purpose

This data repository is used in conjunction with UnitsML.

Sources include:

• BIPM SI Brochure

• NIST SP 811

• ISO 80000 series

• (in some cases, "Encyclopaedia of Scientific Units, Weights and Measures, Their SI Equivalences and Origins" by François Cardarelli, is consulted)

Note	Conversion factors here are not updated with the revised SI.

Structure

This repository contains the following YAML files:

dimensions.yaml

Contains the base dimensions and their symbols.

prefixes.yaml

Contains the SI prefixes and their symbols.

units.yaml

Contains the units and their symbols.

unit_systems.yaml

Contains the unit systems and their symbols.

quantities.yaml

Contains the quantities and their symbols.

Dimensions

General

A dimension object in dimensions.yaml typically has the following structure:

dimension_id:
  {dimension_name}:
    powerNumerator: power_numerator
    symbol: ASCII representation
    dim_symbols:
    - id: dimension_symbol_id
      ascii: ASCII representation
      html: "HTML representation"
      mathml: "MathML representation"
      latex: "LaTeX representation"
      unicode: "Unicode representation"

For example:

NISTd1:
  length:
    powerNumerator: 1
    symbol: L
    dim_symbols:
    - id: dim_L
      ascii: L
      html: "𝖫"
      mathml: "<mi mathvariant='sans-serif'>L</mi>"
      latex: "\\ensuremath{\\mathsf{L}}"
      unicode: "\U0001D5AB"
NISTd2:
  mass:
    powerNumerator: 1
    symbol: M
    dim_symbols:
    - id: dim_M
      ascii: M
      html: "&#x1D5AC;"
      mathml: "<mi mathvariant='sans-serif'>M</mi>"
      latex: "\\ensuremath{\\mathsf{M}}"
      unicode: "\U0001D5AC"

Notes

The following dimensions are identified by NIST but they are excluded from dimensions.yaml since they are unused:

NISTd87:
  dimensionless: true

NISTd86:
  dimensionless: true

NISTd81:
  dimensionless: true

NISTd82:
  dimensionless: true

NISTd83:
  dimensionless: true

NISTd89:
  dimensionless: true

NISTd88:
  dimensionless: true

NISTd91:
  dimensionless: true

NISTd90:
  dimensionless: true

NISTd92:
  dimensionless: true

NISTd93:
  dimensionless: true

Prefixes

General

A prefix object in prefixes.yaml typically has the following structure:

prefix_id:
  name: prefix_name
  symbol:
    ascii: ASCII representation
    html: "HTML representation"
    latex: "LaTeX representation"
    unicode: "Unicode representation"
  base: base
  power: power

For example:

NISTp10_2:
  name: hecto
  symbol:
    ascii: h
    html: h
    latex: h
    unicode: h
  base: 10
  power: 2
NISTp10_1:
  name: deka
  symbol:
    ascii: da
    html: da
    latex: da
    unicode: da
  base: 10
  power: 1

Notes

Decimal prefixes are keyed by their power of 10, e.g. NISTp10_1

The prefix NISTp10_0 is a placeholder for unity.

Binary prefixes are keyed by their power of 2, e.g. NISTp2_10

Quantities

General

A quantity object in quantities.yaml typically has the following structure:

quantity_id:
  dimension_url: "#dimension_id"
  quantity_type: {base|derived}
  quantity_name:
  - quantity_name
  unit_reference:
  - name: unit_name
    url: "#unit_id"

For example:

NISTq8:
  dimension_url: "#NISTd8"
  quantity_type: base
  quantity_name:
  - area
  unit_reference:
  - name: square yard
    url: "#NISTu164"
  - name: square mile
    url: "#NISTu165"
  - name: square meter
    url: "#NISTu1e2/1"
  - name: circular mil
    url: "#NISTu283"
  - name: acre (based on US survey foot)
    url: "#NISTu317"
  - name: are
    url: "#NISTu42"
  - name: barn
    url: "#NISTu43"
  - name: hectare
    url: "#NISTu44"
  - name: square foot
    url: "#NISTu45"
  - name: square inch
    url: "#NISTu46"
NISTq166:
  dimension_url: "#NISTd18"
  quantity_type: derived
  quantity_name:
  - electric potential
  unit_reference:
  - name: atomic unit of electric potential
    url: "#NISTu261"
  - name: statvolt
    url: "#NISTu268"
NISTq7:
  dimension_url: "#NISTd7"
  quantity_type: base
  quantity_name:
  - luminous intensity
  unit_reference:
  - name: candela
    url: "#NISTu7"

Units

General

A unit object in units.yaml typically has the following structure:

unit_id:
  dimension_url: "#dimension_id"
  short: unit_short_name
  root: true
  unit_system:
    type: unit_system_type
    name: unit_system_name
  unit_name:
  - unit_name
  unit_symbols:
  - id: symbol_id
    ascii: ASCII representation
    html: "HTML representation"
    mathml: "MathML representation"
    latex: "LaTeX representation"
    unicode: "Unicode representation"
  root_units:
    enumerated_root_units:
    - unit: unit_name
      power_denominator: power_denominator
      power_numerator: power_numerator
  quantity_reference:
  - name: quantity_name
    url: "#quantity_id"

For example:

NISTu5:
  dimension_url: "#NISTd5"
  short: kelvin
  root: true
  unit_system:
    type: SI_base
    name: SI
  unit_name:
  - kelvin
  unit_symbols:
  - id: K
    ascii: K
    html: K
    mathml: "<mi mathvariant='normal'>K</mi>"
    latex: "\\ensuremath{\\mathrm{K}}"
    unicode: K
  - id: degK
    ascii: degK
    html: "&#176;K"
    mathml: "<mi mathvariant='normal'>&#176;K</mi>"
    latex: "\\ensuremath{\\mathrm{^{\\circ}K}}"
    unicode: "°K"
  root_units:
    enumerated_root_units:
    - unit: kelvin
      power_denominator: 1
      power_numerator: 1
  quantity_reference:
  - name: thermodynamic temperature
    url: "#NISTq5"

Unit systems

General

A unit system object in unit_systems.yaml typically has the following structure:

- id: unit_system_id
  name: unit_system_name
  acceptable: {true|false} # whether the unit system is SI acceptable

For example:

- id: SI_base
  name: SI
  acceptable: true
- id: SI_derived_special
  name: SI
  acceptable: true