In the tool, if you create a QuantityKind in a BDD using the sidebar menu item, it will create an InstanceSpecification that has the QuantityKind stereotype (with keyword «quantityKind») applied and two classifiers QuantityKind and DerivedQuantityKind from the QUDV ModelLibrary:

SysML-1.6: 'A DerivedQuantityKind is a QuantityKind that represents a kind of quantity that is defined as a product of powers of one or more other kinds of quantity. A DerivedQuantityKind may also be used to define a synonym kind of quantity for another kind of quantity.'

This is not always want you want! But you can easily just remove the DerivedQuantityKind classifier and add SimpleQuantityKind.

In the tool, if you create a Unit in a BDD using the sidebar menu item, it will create an InstanceSpecification that has the Unit stereotype (with keyword «unit») applied and two classifiers DerivedUnit and Unit from the QUDV ModelLibrary:

SysML-1.6: 'A DerivedUnit is a Unit that represents a measurement unit that is defined as a product of powers of one or more other measurement units.'

This is not always want you want! But you can easily just remove the DerivedUnit classifier and add SimpleUnit.

Up next

QuantityKind and ValueType example - length vs radius vs radius of tire

Notes

[TIP]{INFORMATIVE} QUDV in SysML refers to: Quantity, Unit, Dimension, Value. It is strongly influenced by the International Vocabulary of Metrology (VIM).

[CAVEAT, TOOL, WORKAROUND] MagicDraw/Cameo: By default assumes custom units are both Unit and DerivedUnit and that quantity kinds are both QuantityKind and DerivedQuantityKind. Just remove the "Derived" variants if they don't apply and add the "Simple" variants.

Snippets (quotes/extracts)

[SysML-1.6] ... a SysML value property is understood to correspond to the VIM concept of "quantity" defined as a "property of a phenomenon, body or substance, where the property has a magnitude that can be expressed as a number and a reference" [VIM3-1.1].

[SysML-1.6] A Unit is a quantity in terms of which the magnitudes of other quantities that have the same quantity kind can be stated.

[SysML-1.6] Unit is defined as a non-abstract SysML Block defined in the SysML UnitAndQuantityKind model library.

[SysML-1.6] Unit, or a specialization of it, classifies an InstanceSpecification to define a particular "measurement unit" in the sense of a "real scalar quantity, defined and adopted by convention, with which any other quantity of the same kind can be compared ...