Specifying Action Types

You can add additional detail to your modeling of activities by specifying the type of action performed and, in certain cases, associating it with a specific model object that it acts upon, and the parameters that it passes.

1. Open the property sheet of an activity and click the Action tab.
2. Select an action type. The following list details the available action types, and specifies where appropriate, the required action object:

   • <Undefined> [no object] - default. No action defined

   • Reusable Activity [no object] – a top-level container.

   • Call [operation or activity] – calls an operation or activity. See Example: Using the Call action type

   • Accept Call [operation or activity] – waits for an operation or activity to be called.

   • Reply Call [operation or activity] – follows an Accept Call action, and responds to an operation or activity.

   • Generate Event [event] – generates an event. Can be used to raise an exception.

   • Accept Event [event] – waits for an event to occur.

   • Create Object [classifier] – creates a new instance of a classifier

   • Destroy Object [classifier] – destroys an instance of a classifier

   • Read Attribute [classifier attribute] – reads an attribute value from a classifier instance

   • Write Attribute [classifier attribute] – writes an attribute value to a classifier instance

   • Read Variable [variable] – writes a value to a local variable. The variable can be used to store an output pin provided by an action to reuse later in the diagram. See Example: Reading and writing variables.

   • Write Variable [variable] - reads a value from a local variable. See Example: Reading and writing variables.

   • Evaluate Expression [expression text] – evaluates an expression and returns the value as an output pin.

   • Unmarshall [no object] – breaks an input object instance into several outputs computed from it.

   • Region [no object] – a composite activity that isolates a part of the graph. Equivalent to the UML Interruptible Activity Region.

   • For Each [no object] – loops an input collection to execute a set of actions specified into the decomposed activity. Equivalent to the UML Expansion Region.

   • Loop Node [expression text] – expression text

3. If the action type requires an action object, an additional field will be displayed directly below the Action Type list, allowing you to specify an activity, classifier, attribute, event, expression, operation, or variable upon which the action acts. You can use the tools to the right of the list to create an object, browse the available objects or view the properties of the currently selected object.
4. Click OK to save your changes and return to the diagram.

• Example: Using the Call Action Type
  One of the most common action types is Call, which allows an activity to invoke a classifier operation (or another activity).
• Example: Reading and Writing Variables
  Variables hold temporary values that can be passed between activities. You can create and access variables using the Write Variable and Read Variables action types