SysML ValueType and QUDV overview

The properties compartment has a Property umlAttribute with a type DataType. While this is permitted in SysML, you should usually avoid such Properties on Blocks:

SysML-1.6: 'Although SysML indirectly imports the UML 2 PrimitiveTypes library ... due to the transitivity of package import, SysML provides a PrimitiveValueTypes model library that systems engineers can extend via SysML’s ValueType stereotype.'

Webel Best Practice: In SysML, unless you MUST use a DataType or PrimitiveType from an existing ModelLibrary or Profile, you SHOULD probably be using a ValueType, Enumeration ValueType, or SysML PrimitiveValueType instead so that it integrates with the value system of SysML.

Both value properties intValue:Integer and realValue:Real use the SysML primitive variants, which then appear as intend in the SysML values compartment.

The value property customValue has a type ValueType, which is a custom ValueType with a custom Unit. Consistent with Webel Best Practice:

Webel Best Practice: SysMLv1.x: ValueType naming: The Webel convention is 'UpperCamelCase' (a.k.a. PascalCase).

While a ValueType can have a unit, it need not always, so it can be used for unitless quantities as for the value property unitlessValue with custom ValueType UnitlessType.

You can also reuse a ValueType and/or Unit from the ISO-80000 ModelLibrary, as shown for the value property s:mass[gram]. Note that:

MagicDraw/Cameo: SysMLv1.x: ValueType naming: The ISO-80000 libraries use 'lower case' (sometimes with spaces for compound units and/or with [scaling] indicated in square brackets).

A Unit has an optional symbol, which can optionally be displayed in the tool in most places where a value property label or symbol can be displayed. Here the value property totalCost has a custom ValueType Cost with a custom unit USD with symbol '$".

Both ValueType and Unit can carry an optional QuantityKind; we'll look at that later in a dedicated advanced tutorial trail section. But first, let's see next how value properties work, and how to use values in a system.

Up next

UML DataType vs SysML ValueType

Notes

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

[TIP]{STRONG} In SysML, unless you MUST use a DataType or PrimitiveType from an existing ModelLibrary or Profile, you SHOULD probably be using a ValueType, Enumeration ValueType, or SysML PrimitiveValueType instead so that it integrates with the value system of SysML.

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

[NAMING, TOOL] MagicDraw/Cameo: SysMLv1.x: ValueType naming: The ISO-80000 libraries use 'lower case' (sometimes with spaces for compound units and/or with [scaling] indicated in square brackets).

Snippets (quotes/extracts)

[SysML-1.6] Value types may be used to type properties, operation parameters, or potentially other elements within SysML.

[SysML-1.6] Although SysML indirectly imports the UML 2 PrimitiveTypes library ... due to the transitivity of package import, SysML provides a PrimitiveValueTypes model library that systems engineers can extend via SysML’s ValueType stereotype.

[SysML-1.6] Four general categories of properties of blocks are recognized in SysML: parts, references, value properties, and constraint properties.

[SysML-1.6] A property typed by a SysML ValueType is classified as a value property, and always has composite aggregation.