# Module Documentation: eml-unitTypeDefinitions | Back to EML Contents

### EML Unit Type Definitions

### Philosophy of Units

The concept of "unit" represents one of the most fundamental categories of metadata. The classic example of data entropy is the case in which a reported numeric value loses meaning due to lack of associated units. Much of Ecology is driven by measurement, and most measurements are inherently comparative. Good data description requires a representation of the basis for comparison, i.e., the unit. In modeling units, the authors of EML drew inspiration from the

#### NIST Reference on Constants, Units, and Uncertainty

. This document defines a unit as "a particular physical quantity, defined and adopted by convention, with which other particular quantities of the same kind are compared to express their value." The authors of the EML 2 specification (hereafter "the authors") decided to make the unit element required, wherever possible.

The units are defined in the

#### STMML language

in a document that is shipped with each release of EML. See the accompanying STMML file, eml-unitDictionary.xml, for precise, quantitative definitions of each of these units and their relationships to base SI units

which modules use these types (and which could but dont yet?)

anything else?

## Module details

Recommended Usage: | any module that needs units
Stand-alone: | no
Imports: | eml-documentation
Imported By: |

## Simple Type Definitions:
### #### StandardUnitDictionary
| The unitDictionary is the standard set of units included with the EML distribution, mainly from the SI standard. These unit names should be used in the standardUnit field to describe an attribute. See the accompanying STMML file, eml-unitDictionary.xml, for precise, quantitative definitions of each of these units and their relationships to base SI units. The standard Unit Dictionary is built from a union of simpleTypes. This construct allows unit types to be used individually as appropriate in EML content (e.g., LengthUnitType for distances )
### #### LengthUnitType
Derived from: xs:string (by xs:restriction) Allowed values: meter nanometer micrometer micron millimeter centimeter decimeter dekameter hectometer kilometer megameter angstrom inch Foot_US foot Foot_Gold_Coast fathom nauticalMile yard Yard_Indian Link_Clarke Yard_Sears mile | The LengthUnitType is the enumerated list of units which are of length type, or have a parentSI of meter. These unit names can be used where ever content should be restricted to a length, such as a distance or altitude. The units are defined in the STMML language in a document that is shipped with each release of EML called eml-unitDictionary.xml. See this file for precise, quantitative definitions of each of these units and their relationships to base SI units.
### #### MassUnitType
Derived from: xs:string (by xs:restriction) Allowed values: kilogram nanogram microgram milligram centigram decigram gram dekagram hectogram megagram tonne pound ton | The MassUnitType is the enumerated list of units which are of mass type, or have a parentSI of kilogram. These unit names can be used where ever content should be restricted to a mass, such as an amount. The units are defined in the STMML language in a document that is shipped with each release of EML called eml-unitDictionary.xml. See this file for precise, quantitative definitions of each of these units and their relationships to base SI units.
### #### otherUnitType
Derived from: xs:string (by xs:restriction) Allowed values: dimensionless second kelvin coulomb ampere mole candela number radian degree grad cubicMeter nominalMinute nominalHour nominalDay nominalWeek nominalYear nominalLeapYear celsius fahrenheit nanosecond microsecond millisecond centisecond decisecond dekasecond hectosecond kilosecond megasecond minute hour kiloliter microliter milliliter liter gallon quart bushel cubicInch pint megahertz kilohertz hertz millihertz newton joule calorie britishThermalUnit footPound lumen lux becquerel gray sievert katal henry megawatt kilowatt watt milliwatt megavolt kilovolt volt millivolt farad ohm ohmMeter siemen weber tesla pascal megapascal kilopascal atmosphere bar millibar kilogramsPerSquareMeter gramsPerSquareMeter milligramsPerSquareMeter kilogramsPerHectare tonnePerHectare poundsPerSquareInch kilogramPerCubicMeter milliGramsPerMilliLiter gramsPerLiter milligramsPerCubicMeter microgramsPerLiter milligramsPerLiter gramsPerCubicCentimeter gramsPerMilliliter gramsPerLiterPerDay litersPerSecond cubicMetersPerSecond cubicFeetPerSecond squareMeter are hectare squareKilometers squareMillimeters squareCentimeters acre squareFoot squareYard squareMile litersPerSquareMeter bushelsPerAcre litersPerHectare squareMeterPerKilogram metersPerSecond metersPerDay feetPerDay feetPerSecond feetPerHour yardsPerSecond milesPerHour milesPerSecond milesPerMinute centimetersPerSecond millimetersPerSecond centimeterPerYear knots kilometersPerHour metersPerSecondSquared waveNumber cubicMeterPerKilogram cubicMicrometersPerGram amperePerSquareMeter amperePerMeter molePerCubicMeter molarity molality candelaPerSquareMeter metersSquaredPerSecond metersSquaredPerDay feetSquaredPerDay kilogramsPerMeterSquaredPerSecond gramsPerCentimeterSquaredPerSecond gramsPerMeterSquaredPerYear gramsPerHectarePerDay kilogramsPerHectarePerYear kilogramsPerMeterSquaredPerYear molesPerKilogram molesPerGram millimolesPerGram molesPerKilogramPerSecond nanomolesPerGramPerSecond kilogramsPerSecond tonnesPerYear gramsPerYear numberPerMeterSquared numberPerKilometerSquared numberPerMeterCubed numberPerLiter numberPerMilliliter metersPerGram numberPerGram gramsPerGram microgramsPerGram cubicCentimetersPerCubicCentimeters | The unitDictionary is the standard set of units included with the EML distribution, mainly from the SI standard. These unit names can be used in the standardUnit field to describe an attribute. The units are defined in the STMML language in a document that is shipped with each release of EML. See the accompanying STMML file eml-unitDictionary.xml for precise, quantitative definitions of each of these units and their relationships to base SI units. The standard Unit Dictionary is built from a union of simpleTypes. This Type enumerates the units which are not in other Type definitions, but are to be included as standard.
### #### angleUnitType
Derived from: xs:string (by xs:restriction) Allowed values: radian degree grad | The AngleUnitType is the enumerated list of angle units. For example, plane angle (radian, rad) and solid angle (steradian, sr) are actually dimensionless, and their symbols used as appropriate (e.g, sr in photometry). These unit names could be used where ever content should be restricted.

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