19.3. Stimulus

19.3. Stimulus
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A stimulus is a communication between two instances and is generated by an action. On a sequence diagram a stimulus is associated with a link -an instance of an association linking two object instances. In the UML metamodel Stimulus is a sub-class of ModelElement.

The link (see Section 19.9, “ Link ”) associated with a stimulus is represented on a sequence diagram in ArgoUML as an arrow between the time lines of the object instances (or the object head in the case of stimulus create, described below) labeled with the name of the action (if any), and the action, separated by a colon (:). The type of line and arrowhead depends on the type of action that generated the stimulus:

Stimulus Call. Generated by a call action, itself the result of an operation of a class. Shown as a solid line with a solid arrowhead to the time line of the object instance receiving the stimulus.
Stimulus Create. Generated by a create action for the class for which an instance is to be created Shown as a solid line with a solid arrowhead to the object head of the object instance being created.
Stimulus Destroy. Generated by a destroy action of the originating object. Shown as a solid line with an open arrowhead terminating in a diagonal cross at the end of the time line of the receiving (destroyed) object instance.
Stimulus Send. Generated by a send action, the result of a signal raised by an operation of the sending object instance and handled by the receiving object instance. Shown as a solid line with half an open arrowhead.
Stimulus Return. Generated by an object instance that has received an earlier call stimulus and is returning a result to the calling object instance. Shown as a dotted line with an open arrowhead.

	Note
	ArgoUML does not allow you to create stimuli directly, but instead provides tools to create stimuli of each of the five types above.

Caution

In the current release of ArgoUML there is no way to show a terminate action where an object instance destroys itself. One way is to draw a destroy action that loops back to the object itself, give it an action with no name and use the style tab to set an invisible line, but this still leaves the arrow head showing, which is unsightly. It is also semantically incorrect anyway to use a destroy action to represent a terminate action.

19.3.1. Stimulus Details Tabs

The details tabs that are active for stimuli are as follows.

ToDoItem

Standard tab.

Properties

See Section 19.3.2, “ Stimulus Property Toolbar ” and Section 19.3.3, “ Property Fields For Stimulus ” below.

Documentation

Standard tab.

Style

Standard tab. The values for the bounds of the stimulus notionally define the bounding box of the stimulus and its time line. However if you change them it will have no effect, and the original values will be reset when you next revisit the tab.

Altering the Fill and Shadow entries has no effect. Rather bizarrely you can set the Line entry and it will draw a line around the signal, which is not a standard UML representation.

	Tip
	To change the color of the line, you should select the associated link (click on it a little way from the stimulus) and use its style tab (see Section 19.9, “ Link ”).

	Caution
	In the current release of ArgoUML changing the values of the `Bounds` field is possible, but will make only a temporary change to the position of the stimulus. Selecting any model element on the screen causes the stimulus to return to its original position and the original values to be restored.

Source

Standard tab, but with no contents.

	Caution
	A stimulus should not generate any code, so having this tab active is probably a mistake.

Constraints

Standard tab. ArgoUML only supports constraints on Classes and Features (Attributes, Operations, Receptions, and Methods), so this tab is grayed out.

Tagged Values

Standard tab. In the UML metamodel, Stimulus has the following standard tagged values defined.

derived (from the superclass, ModelElement). Values true, meaning the stimulus is redundant -it can be formally derived from other elements, or false meaning it cannot.

	Note
	Derived stimuli still have their value in analysis and design to introduce useful names or concepts, and in design to avoid re-computation.

	Note
	The UML `Element` metaclass from which all other model elements are derived includes the tagged element `documentation` which is handled by the documentation tab under ArgoUML

19.3.2. Stimulus Property Toolbar

Go up

Navigate up through the package structure.

Delete

This deletes the stimulus from the model

	Warning
	This is a deletion from the model not just the diagram. To delete an stimulus from the diagram, but keep it within the model, use the main menu `Remove From Diagram` (or press the Delete key).

19.3.3. Property Fields For Stimulus

Name

Text box. There is no convention for naming stimuli, and it is quite normal to leave them unnamed. The action is sufficient identification.

	Tip
	It is sometimes useful to give simple names to stimuli, so they can be referred to in attached notes giving timing constraints.

Action

Text box. This is used to identify the action that generated the stimulus.

Caution

The current release of ArgoUML only implements actions as textual descriptions.

As a practical convention it is suggested that call actions are shown as the name of the operation generating the action with any arguments in parentheses and that send actions are shown as the name of the signal generating the action with any arguments in parentheses. Return actions should be shown as the expression for the value they return, or empty otherwise. Create and destroy actions should be left empty, since they are implied by their representation.

Stereotype

Drop down selector. Stimulus has no stereotypes by default in the UML standard, but ArgoUML provides the stereotypes, machine, organization and person.

	Caution
	ArgoUML also provides the stereotype `realize` for stimuli. This appears to be an error, since this stereotype properly belongs to the `Abstraction` metaclass.

Navigate Stereotype

icon. If a stereotype has been selected, this will navigate to the stereotype property panel (see Section 18.5, “ Stereotype ”).

Sender

Text box. Identifies the instance which sent this stimulus.

Button 1 click navigates to the sender instance, button 2 gives a pop up menu with one entry.

Open. Navigate to the selected sender instance.

Receiver

Text box. Identifies the instance which receives this stimulus.

Button 1 click navigates to the receiver instance, button 2 gives a pop up menu with one entry.

Open. Navigate to the selected receiver instance.

	Warning
	In the current release of ArgoUML this field is broken. It always shows the entry `none` and the pop-up menu is grayed out.

Namespace

Text box. Records the namespace for the stimulus. This is the package hierarchy.

Button 1 click on the entry will navigate to the package defining this namespace (or the model for the top level namespace).

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