This version:
Previous published version: https://qudt.org/doc/2025/02/DOC_SCHEMA-SHACL-QUDT.html
Editor: Ralph Hodgson, TopQuadrant, Inc
Contributors: Daniel Mekonnen, David Price, Jack Hodges, James E. Masters, Simon J D Cox, Steve Ray
Last Modified: 2025-03-20T15:47:09Z
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The QUDT, or "Quantity, Unit, Dimension and Type" schema defines the base classes properties, and restrictions used for modeling physical quantities, units of measure, and their dimensions in various measurement systems. The goal of the QUDT ontology is to provide a unified model of, measurable quantities, units for measuring different kinds of quantities, the numerical values of quantities in different units of measure and the data structures and data types used to store and manipulate these objects in software.
Except for unit prefixes, all units are specified in separate vocabularies. Descriptions are provided in both HTML and LaTeX formats. A quantity is a measure of an observable phenomenon, that, when associated with something, becomes a property of that thing; a particular object, event, or physical system.
A quantity has meaning in the context of a measurement (i.e. the thing measured, the measured value, the accuracy of measurement, etc.) whereas the underlying quantity kind is independent of any particular measurement. Thus, length is a quantity kind while the height of a rocket is a specific quantity of length; its magnitude that may be expressed in meters, feet, inches, etc. Or, as stated at Wikipedia, in the language of measurement, quantities are quantifiable aspects of the world, such as time, distance, velocity, mass, momentum, energy, and weight, and units are used to describe their measure. Many of these quantities are related to each other by various physical laws, and as a result the units of some of the quantities can be expressed as products (or ratios) of powers of other units (e.g., momentum is mass times velocity and velocity is measured in distance divided by time).
The namespace prefix for resources in this ontology is: qudt
The http://www.linkedmodel.org/schema/vaem#shaclschemagraph is available as:
Turtle
A list of graphs imported by http://qudt.org/3.1.0/schema/shacl/qudt is shown below.
| Graph URI | Intent |
|---|---|
| http://qudt.org/3.1.0/schema/shacl/datatype | |
| http://qudt.org/3.1.0/schema/shacl/overlay/qudt | Specifies overlay properties and rules for the schema for quantities, units and dimensions. Types are defined in other schemas. |
| http://www.linkedmodel.org/schema/dtype | The purpose of DTYPE is to provide, by import, a foundation for data types. |
| http://www.linkedmodel.org/schema/vaem | The purpose of VAEM is to provide, by import, a foundation for commonly needed resources for metadata on an ontology. |
| http://www.w3.org/2004/02/skos/core | |
| http://www.w3.org/ns/shacl# |
The graph uses 10 resources from other graphs that are not imported, as listed below:
The main namespace for resources in this graph is http://qudt.org/schema/qudt/ with the prefix qudt.
No Classes defined in this graph
The graph defines, or extends, 136 properties, as indexed below:
The graph defines, or extends, 2 instances, as indexed below:
The graph defines, or extends, 2 restricted datatypes, as indexed below:
qudt:abbreviation
An abbreviation for a unit is a short ASCII string that is used in place of the full name for the unit in contexts where non-ASCII characters would be problematic, or where using the abbreviation will enhance readability. When a power of abase unit needs to be expressed, such as squares this can be done using abbreviations rather than symbols. For example, sq ft means square foot, and cu ft means cubic foot.
qudt:applicableUnit
See this page on the QUDT GitHubWiki on how "qudt:applicableUnit" is computed from "qudt:hasQuantityKind" and then materialized.
qudt:baseDimensionEnumeration
This property associates a system of quantities with an enumeration that enumerates the base dimensions of the system in canonical order.
qudt:baseUnitOfSystem
This property relates a unit of measure to the system of units in which it is defined as a base unit for the system. The base units of a system are used to define the derived units of the system by expressing the derived units as products of the base units raised to a rational power.
qudt:coherentUnitSystem
A system of units is coherent with respect to a system of quantities and equations if the system of units is chosen in such a way that the equations between numerical values have exactly the same form (including the numerical factors) as the corresponding equations between the quantities. In such a coherent system, no numerical factor other than the number 1 ever occurs in the expressions for the derived units in terms of the base units. For example, the $newton$ and the $joule$. These two are, respectively, the force that causes one kilogram to be accelerated at 1 metre per (1) second per (1) second, and the work done by 1 newton acting over 1 metre. Being coherent refers to this consistent use of 1. In the old c.g.s. system , with its base units the centimetre and the gram, the corresponding coherent units were the dyne and the erg, respectively the force that causes 1 gram to be accelerated at 1 centimetre per (1) second per (1) second, and the work done by 1 dyne acting over 1 centimetre. So $1\,newton = 10^5 dyne$, $1 joule = 10^7 erg$, making each of the four compatible in a decimal sense within its respective other system, but not coherent therein.
qudt:currencyCode
Alphabetic Currency Code as defined by ISO 4217. For example, the currency code for the US dollar is USD.
qudt:currencyExponent
The currency exponent indicates the number of decimal places between a major currency unit and its minor currency unit. For example, the US dollar is the major currency unit of the United States, and the US cent is the minor currency unit. Since one cent is 1/100 of a dollar, the US dollar has a currency exponent of 2. However, the Japanese Yen has no minor currency units, so the yen has a currency exponent of 0.
qudt:currencyNumber
Three-digit Currency Code as defined by ISO 4217. For example, the currency number for the US dollar is "840".
qudt:definedUnitOfSystem
This property relates a unit of measure with the unit system that defines the unit.
qudt:derivedCoherentUnitOfSystem
This property relates a unit of measure to the unit system in which the unit is derived from the system's base units with a proportionality constant of one.
qudt:derivedNonCoherentUnitOfSystem
This property relates a unit of measure to the unit system in which the unit is derived from the system's base units without proportionality constant of one.
qudt:derivedUnitOfSystem
This property relates a unit of measure to the system of units in which it is defined as a derived unit. That is, the derived unit is defined as a product of the base units for the system raised to some rational power.
qudt:example
The 'qudt:example' property is used to annotate an instance of a class with a reference to a concept that is an example. The type of this property is 'rdf:Property'. This allows both scalar and object ranges.
qudt:expression
An 'expression' is a finite combination of symbols that are well-formed according to rules that apply to units of measure, quantity kinds and their dimensions.
qudt:hasAllowedUnit
This property relates a unit system with a unit of measure that is not defined by or part of the system, but is allowed for use within the system. An allowed unit must be convertible to some dimensionally eqiuvalent unit that is defined by the system.
qudt:hasBaseUnit
This property relates a system of units to a base unit defined within the system. The base units of a system are used to define the derived units of the system by expressing the derived units as products of the base units raised to a rational power.
qudt:hasCoherentUnit
A coherent unit of measurement for a unit system is a defined unit that may be expressed as a product of powers of the system's base units with the proportionality factor of one.
qudt:hasDefinedUnit
This property relates a unit system with a unit of measure that is defined by the system.
qudt:hasDerivedUnit
This property relates a system of units to a unit of measure that is defined within the system in terms of the base units for the system. That is, the derived unit is defined as a product of the base units for the system raised to some rational power.
qudt:hasUnit
This property relates a factor unit to its unit or system of units with a unit of measure that is either:
Systems of units may distinguish between base and derived units. Base units are the units which measure the base quantities for the corresponding system of quantities. The base units are used to define units for all other quantities as products of powers of the base units. Such units are called derived units for the system.
qudt:id
The "qudt:id" is an identifier string that uniquely identifies a QUDT concept. The identifier is constructed using a prefix. For example, units are coded using the pattern: "UCCCENNNN", where "CCC" is a numeric code or a category and "NNNN" is a digit string for a member element of that category.
For scaled units there may be an addition field that has the format "QNN" where "NN" is a digit string representing an exponent power, and "Q" is a qualifier that indicates with the code "P" that the power is a positive decimal exponent, or the code "N" for a negative decimal exponent, or the code "B" for binary positive exponents.
qudt:informativeReference
Provides a way to reference a source that provided useful but non-normative information.
qudt:isDeltaQuantity
This property is used to identify a Quantity instance that is a measure of a change, or interval, of some property, rather than a measure of its absolute value. This is important for measurements such as temperature differences where the conversion among units would be calculated differently because of offsets.
qudt:isUnitOfSystem
This property relates a unit of measure with a system of units that either a) defines the unit or b) allows the unit to be used within the system.
qudt:isoNormativeReference
Provides a way to reference the ISO unit definition.
qudt:latexSymbol
The symbol is a glyph that is used to represent some concept, typically a unit or a quantity, in a compact form. For example, the symbol for an Ohm is $ohm$. This contrasts with 'unit:abbreviation', which gives a short alphanumeric abbreviation for the unit, 'ohm' for Ohm.
qudt:normativeReference
Provides a way to reference information that is an authorative source providing a standard definition
qudt:plainTextDescription
A plain text description is used to provide a description with only simple ASCII characters for cases where LaTeX , HTML or other markup would not be appropriate.
qudt:quantity
a property to relate an observable thing with a quantity (qud:Quantity)
qudt:relativeStandardUncertainty
The relative standard uncertainty of a measurement is the (absolute) standard uncertainty divided by the magnitude of the exact value.
qudt:relevantUnit
This property is used for qudt:Discipline instances to identify the Unit instances that are used within a given discipline.
qudt:standardUncertainty
The standard uncertainty of a quantity is the estimated standard deviation of the mean taken from a series of measurements.
qudt:standardUncertaintySN
The standard uncertainty of a quantity is the estimated standard deviation of the mean taken from a series of measurements.
qudt:symbol
The symbol is a glyph that is used to represent some concept, typically a unit or a quantity, in a compact form. For example, the symbol for an Ohm is $ohm$. This contrasts with 'unit:abbreviation', which gives a short alphanumeric abbreviation for the unit, 'ohm' for Ohm.
qudt:ucumCode
ucumCode associates a QUDT unit with its UCUM code (case-sensitive).
In SHACL the values are derived from specific ucum properties using 'sh:values'.
qudt:udunitsCode
The UDUNITS package supports units of physical quantities. Its C library provides for arithmetic manipulation of units and for conversion of numeric values between compatible units. The package contains an extensive unit database, which is in XML format and user-extendable. The package also contains a command-line utility for investigating units and converting values.
qudt:uneceCommonCode
The UN/CEFACT Recommendation 20 provides three character alphabetic and alphanumeric codes for representing units of measurement for length, area, volume/capacity, mass (weight), time, and other quantities used in international trade. The codes are intended for use in manual and/or automated systems for the exchange of information between participants in international trade.
qudt:value
A property to relate an observable thing with a value expressed as a decimal
qudt:valueSN
A property to relate an observable thing with a value expressed in scientific notation
vaem:GMD_SHACLQUDT-SCHEMA
URI: http://www.linkedmodel.org/schema/vaem#GMD_SHACLQUDT-SCHEMA
The QUDT, or "Quantity, Unit, Dimension and Type" schema defines the base classes properties, and restrictions used for modeling physical quantities, units of measure, and their dimensions in various measurement systems. The goal of the QUDT ontology is to provide a unified model of, measurable quantities, units for measuring different kinds of quantities, the numerical values of quantities in different units of measure and the data structures and data types used to store and manipulate these objects in software.
Except for unit prefixes, all units are specified in separate vocabularies. Descriptions are provided in both HTML and LaTeX formats. A quantity is a measure of an observable phenomenon, that, when associated with something, becomes a property of that thing; a particular object, event, or physical system.
A quantity has meaning in the context of a measurement (i.e. the thing measured, the measured value, the accuracy of measurement, etc.) whereas the underlying quantity kind is independent of any particular measurement. Thus, length is a quantity kind while the height of a rocket is a specific quantity of length; its magnitude that may be expressed in meters, feet, inches, etc. Or, as stated at Wikipedia, in the language of measurement, quantities are quantifiable aspects of the world, such as time, distance, velocity, mass, momentum, energy, and weight, and units are used to describe their measure. Many of these quantities are related to each other by various physical laws, and as a result the units of some of the quantities can be expressed as products (or ratios) of powers of other units (e.g., momentum is mass times velocity and velocity is measured in distance divided by time).
vaem:QUDT
URI: http://www.linkedmodel.org/schema/vaem#QUDT
QUDT is a non-profit organization that governs the QUDT ontologies.
qudt:LatexString
A type of string in which some characters may be wrapped with '$' and '$ characters for LaTeX rendering.
qudt:UCUMcs
Lexical pattern for the case-sensitive version of UCUM code