UML Activity Diagrams

UML Activity Diagrams
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Overview

Purpose:
- Describe a task/procedure/process
Components:
- Activity - a non-atomic (i.e., decomposable) task
- Action - an atomic (i.e., not decomposable) task
- Data - inputs to or outputs from actions (and may include state information in square brackets)
- Flow - flow of control and flow of data

Symbology

Representation and Interpretation

Directed Graph:
- Nodes/Vertexes - represent actions or objects
- Edges/Arcs/Links - represent control flows and/or data flows
Tokens:
- Produced and consumed by nodes (though not represented on the diagram)
- Flow instantaneously along edges
Execution:
- An action node begins executing when tokens are available on all incoming edges
- When an action node begins execution it consumes all incoming tokens
- While/after an action node executes it produces outgoing tokens

An Example

Additional Elements

Initial Node:
Final Node:
Decision Node:
- One incoming edge
- One or more outgoing edges
- Outgoing edges can have a Boolean guard
Merge Node:
- One or more incoming edges
- One outgoing edge

An Example Revisited

Why Use Merge Nodes?

Still More Elements

Pin:
- A terminator for data flows into (input pins) or out of (output pins) an action node
Activity Parameter:
- An object node on the boundary of an activity
- Contains the name of a particular object and the name of its type
- Syntax: name:type

A Larger Example

Courtesy of Introduction to Software Engineering and Design (Fox, 2006)

The Larger Example with Object/Data Nodes

Sequential and Parallel Actions

Fork Node:
- Splits a single (incoming) flow into multiple concurrent/parallel (outgoing) flows
Join Node:
- Synchronizes multiple (incoming) flows into a single (outgoing) flow

An Example with Parallel Actions

Compare the Following Activity Diagrams

Abstraction and Sub-Activities

Abstraction in Activity Diagrams:
- As with any model, a decision must be made about how much detail to include
Associating an Activity with an Action:
- It's possible to indicate that a sub-activity exists for an action using the following notation: