Chapter 11Activity Diagrams

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• “Activity diagrams are a technique to describe procedural logic, business processes, and work flows” - M. Fowler

• An activity diagram... – models the dynamic aspects of a system.

– serves the same function as a flowchart.

– Is composed of a sequence of actions, possibly concurrent

Introduction

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• An activity diagram…– is commonly used to show the actions/steps involved in

carrying out a particular use-case.

– Shows the flow from action to action.

– Commonly contains action states, flows (a.k.a edges and transitions), forks, merges, joins, decisions and objects.

• Decisions…– are used to show alternate flows of control.

– is represented as a diamond. Outgoing transitions are labeled with guard conditions.

Terms and Concepts

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• Forking and Joining– A fork is when a single flow of control splits into two

or more parallel (concurrent) flows of control.

– A join is when two or more flows of control merge into a single flow of control.

– A flow of control is also known as a thread.

– A synchronization bar is used to model forking and joining, and is modeled as a thick horizontal or vertical bar.

Terms and Concepts

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A Simple Activity DiagramFigure 11.1

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• Actions can be decomposed into subactivities– Used as a way to manage complexity

– Indicated by the rake symbol

Decomposing an Action

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The Activity Diagram of Figure 11.1 modified to invoke the activity in figure 11.2

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• Partitions...– Are used to group actions according to the organization

or class responsible for those actions.

– Are divided by solid vertical lines.

– Can be used in the context of concurrency.

• An activity can only belong to one partition, but transitions between actions may cross partitions.

Partitions (a.k.a. Swimlanes)

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Activity Diagram with Partitions

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Receiving Signals

• A signal is an event received from an outside process.

• The receipt of the signal triggers the start of an activity

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Sending Signals

The activity sends a signal (send itinerary) and then concurrently waits for two separate external signals. The first flow to reach the final state will terminate the other flow.

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Tokens

“Control flow is modeled in terms of tokens. The start node will create a token which then goes to next action. After the action executes, the token will go to the next action. When it encounters a fork, the fork will create a token for each of its outbound flows. The opposite happens for joins. It will produce an outbound token once all inbound tokens arrived.” -- http://edutechwiki.unige.ch/en/UML_activity_diagram

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Four Ways of Showing an Edge(an edge is another name for transition)

The last two examples are passing an Order object from Receive Invoice to Make Payment

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Pins and Transformations

• Actions can have parameters

• Parameters can be modeled as pins

• Pins correspond to the parameter boxed on a decomposed diagram

• Transformations can be used to ensure arguments match parameters

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Expansion Region

• An expansion region marks an activity diagram area where actions occur once for each item in a collection

• Once all of the reviewed articles have been placed in the list box pin, a single token is passed to Publish Newsletter

• <<concurrent>> or <<iterative>> stereotypes are commonly used

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Expansion Region

• Prepare Article is a shorthand notation for the expansion region in figure 11.9

• <<concurrent>> expansion is assumed by default

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Flow Finals

• Within an expansion region a final flow indicates the end of a particular flow with out termination the remaining flows.

• The number of items in the output collection may be less than the number of items in the input collection

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Join Specification

• A join specification is a Boolean expression attached to a join

• Each time a token arrives at the join, the join specification is evaluated

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• Object Flow– Objects may be attached (using dependencies) to

specific activities in an activity diagram.

– The activity to which an object is connected has a direct effect on the object’s state or lifetime.

– An object’s state may be shown in brackets inside the object rectangle.

Objects and Activity Diagrams

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Activity Diagram with Object Flow Using UML 1 Notation