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

The links typed by Associations are only shown to reveal some of the underlying QUDV machinery, you don't need those to create your own Units and ValueTypes.

The SimpleQuantityKind length from the QUVD ModelLibrary has the SimpleUnit metre. Another SimpleQuantityKind radius is linked to it, corresponding to an Association in the QUVD ModelLibrary that has one end 'general', which appears on the radius instance as a Slot assigned the value length (noting Generalization can't be used with instances).

Both length and radius are linked to the same SystemOfQuantities instance ISO 80000-3 Quantities.

Generalization can be used with ValueType to reuse and adapt radius. Why extend ? Here's just one possible reason:

You can use a ValueType to document how a value of a certain quantity kind should be measured (in a particular system, in a particular organisation, or according to an industry standard).

For example, one might document the pressure and seating of a tire for standard measurement of its outer radius.

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QuantityKind and ValueType example - frequency vs clock frequency vs sound frequency

Notes

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

[NAMING, POLICY]{STRICT} SysMLv1.x: ValueType naming: The Webel convention is 'UpperCamelCase' (a.k.a. PascalCase).

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.