SysML, UAF, UML, and UPDM Profiles > SysML profile > Blocks > Quantity kinds, units and value types > Units > Unit (SysML item)
Unit (SysML item)
A Unit is a quantity in terms of which the magnitudes of other quantities that have the same quantity kind can be stated. A unit often relies on precise and reproducible ways to measure the unit. For example, a unit of length such as meter may be specified as a multiple of a particular wavelength of light. A Unit may also specify less stable or precise ways to express some value, such as a cost expressed in some currency, or a severity rating measured by a numerical scale.
Create a Unit through a Modeler explorer pane or a Block Definition Diagram:
• In a Modeler pane, right-click the Model or Package that is to own the Unit, point to New, point to SysML, point to Structure, and then click Unit.
• On a Block Definition Diagram, click the Unit button, and then click in free space.
A Unit can use a single Quantity Kind: right-click the Unit, point to Links, click Quantity Kind, and then select the appropriate Quantity Kind (if the Unit already has a Quantity Kind, that Quantity Kind is replaced). The Unit tab of the Unit's property pages lists the selected Quantity Kind.
A Unit can be used by a Value Type: right-click the Value Type, point to Links, click Unit, and then select the Unit.
When shown on a Block Definition Diagram, a Unit's notation is as follows:
To populate a Block Definition Diagram with Units that are in the same Package as the diagram: on the diagram, right-click in free space, point to Populate, point to Nodes, and then click Units.
You can right-click a Unit on a Block Definition Diagram, and through the commands on the Populate submenu, populate links that exist between the Unit and other items.
The SysML profile includes standard SI Definition Units that you can use, such as Hertz, Newton and Watt - the SI Definition Units are provided in sub-Packages of the SI Definitions package.
All Units are shown in the Blocks pane - expand the Unit folder.
A Unit is a UML Class that is stereotyped by the «Unit» stereotype from the SysML profile.
The following sections provide information about how a Unit is used in the model. For more information about a SysML diagram or item - click it.
Owned by
Model (UML item)
Package (UML item)
Owns
Allocate - the Allocate is owned jointly by the Unit and the associated item. The access permissions you have to an Allocate are determined by the access permissions you have to the item that is allocated from - you require write access to both items to create or delete an Allocate.
Generalization (UML item) - the Generalization is owned jointly by the two Units it links. The access permissions you have to a Generalization are determined by the access permissions you have to the sub Unit.
Problem
Rationale
Refine (UML Standard profile) - the Refine relationship is owned jointly by the Unit and the associated item. The access permissions you have to a Refine relationship are determined by the access permissions you have to the refined item.
Satisfy - the Satisfy relationship is owned jointly by the Unit and the associated Requirement. The access permissions you have to a Satisfy relationship are determined by the access permissions you have to the Unit.
Trace (UML Standard profile) - the Trace relationship is owned jointly by the Unit and the associated item. The access permissions you have to a Trace relationship are determined by the access permissions you have to the item that is traced from.
Verify - the Verify relationship is owned jointly by the Unit and the associated Requirement. The access permissions you have to a Verify relationship are determined by the access permissions you have to the Unit.
Shown on these diagrams
Block Definition Diagram
SysML Properties
• allocatedFrom - lists source items that are linked through Allocate relationships (on Allocated tab when item is allocated).
• allocatedTo - lists target items that are linked through Allocate relationships (on Allocated tab when item is allocated).
• quantityKind - lists the Quantity Kind that is used by the Unit.