Instances with part-carrying Slots

If the definingFeature of a Slot is typed by a Block - i.e. if it is a block property that is part property or a reference property - the Slot will carry an instance of a Block, the Slots of which may in turn carry simple values or other block properties:

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Dependency relationships indicating Types in this diagram are for illustration only

Note that the defaultValue of any block property (part property or reference property) may also be a instance typed by a Block; this mechanism is extremely important for representing value configurations of systems.

(We'll see later how this can be used for representing "deep" configurations of a system using the SysML context-specific values mechanism; but for now, we'll just examine one level of value configuration.)

You can use a "link" (a special form of InstanceSpecification) to relate two instances together; the tool also knows how to identify and match Slots and any candidate Associations, and it will prompt you to perform Slot assignments and choose a compatible Association if one exists.

In the example, there is a link :OB-BWV from defaultOuter:OuterBlock to instance defaultPart:BlockWithValues, which has been assigned to the Slot 'part'. The link is typed by the Association OB-BWV.

The instance defaultPart:BlockWithValues also has Slots for each of the Features of BlockWithValues, but it has overridden all of the default values! So one level of re-configuration has been performed in the context of BlockWithValues through assignment of defaultPart:BlockWithValues as the default 'part'.

You don't have to use explicit links, you can just assign to the Slots directly (which approach one might use if there is no explicit Association). One can reinforce the assignment using visual nesting, but please be aware that:

Visual nesting of InstanceSpecification symbols has no meaning in the underlying model, only assignment to a Slot does!

The visual nesting of instance customPart:BlockWithValues within customOuter:OuterBlock indeed corresponds to the assignment of customPart:BlockWithValues to the 'part' Slot of customOuter:OuterBlock, but that's purely a drawing device.

The Slot 'part' of instance customOuter:OuterBlock has overridden the default 'part' with an instance customPart:BlockWithValues, which has in turn redefined all value Slots. So we have a 2nd level of value re-configuration.

Up next

Block level :values and :properties compartments in IBD

Notes

[ASSERTION, WARNING]{STRICT} Visual nesting of InstanceSpecification symbols has no meaning in the underlying model, only assignment to a Slot does!

[FEATURE, TIP, TOOL]{SUGGESTED} MagicDraw/Cameo: When you create an InstanceSpecification in a diagram it will a Select Classifier dialog. It is often faster to Cancel that and then just drag a Classifier onto the instance symbol from the diagram or model tree.

[DISPLAY, FEATURE, TOOL]{INFORMATIVE} MagicDraw/Cameo: If you want to show a Property or Port listed both in its corresponding compartment on a Class or Block symbol and as the end of an Association in the same diagram, set the display option Show Association Ends As Attributes/Ports to 'all'

Snippets (quotes/extracts)

[UML-2.5.1] An InstanceSpecification is a model element that represents an instance in a modeled system.

[UML-2.5.1] InstanceSpecification::classifer : Classifier [0..*] ... The Classifier or Classifiers of the represented instance. If multiple Classifiers are specified, the instance is classified by all of them.

[UML-2.5.1] InstanceSpecification::slot : Slot [0..*] ... A Slot giving the value or values of a StructuralFeature of the instance. An InstanceSpecification can have one Slot per StructuralFeature of its Classifiers, including inherited features. ...

[UML-2.5.1] InstanceSpecification::slot : Slot [0..*] ... It is not necessary to model a Slot for every StructuralFeature, in which case the InstanceSpecification is a partial description.

[SysML-1.6] A Slot designates that an entity modeled by an InstanceSpecification has a value or values for a specific StructuralFeature.